130 Science Words That Start With A (With Meanings)

Understanding science becomes easier when you know the right words Science Words That Start With A. This guide shares 130 science words that start with A, grouped by topic. Whether you’re a student, teacher, or just curious, this is the perfect science words list to help you grow your science vocabulary.

Science terms can be confusing. But learning them alphabetically makes it simple. Let’s explore science words and definitions starting with the letter A, one field at a time Science Words That Start With A.

Biology & Life Sciences

Word	Meaning	Example
Abiotic	Non-living parts of an ecosystem	Sunlight is an abiotic factor in a desert.
Aerobic	Needing oxygen to survive or grow	Humans are aerobic organisms.
Anaerobic	Not needing oxygen to survive	Some bacteria grow in anaerobic environments.
Allele	A version of a gene	Eye color is controlled by different alleles.
Adaptation	A change that helps a species survive	Camouflage is an adaptation in many animals.
Anatomy	The study of body structure	We learned about human anatomy in biology class.
Arthropod	Animals with exoskeletons and jointed legs	Spiders are arthropods.
Autotroph	An organism that makes its own food	Plants are autotrophs using sunlight.
Asexual	Reproduction without involving two parents	Some plants reproduce asexually by cloning.
Amniotic	Related to the protective fluid around embryos	The fetus floats in the amniotic sac.

Chemistry

Word	Meaning	Example
Atom	The smallest unit of matter	Everything is made up of atoms.
Anion	A negatively charged ion	Chloride is an example of an anion.
Alkali	A base that dissolves in water	Sodium hydroxide is an alkali.
Acid	A substance with a pH less than 7	Vinegar is an acid.
Alloy	A mixture of metals	Bronze is an alloy of copper and tin.
Aromatic	A compound with a ring-like molecular structure	Benzene is an aromatic compound.
Alkaline	Having basic properties (opposite of acidic)	Alkaline substances feel slippery.
Amorphous	A substance without a clear shape or structure	Glass is an amorphous solid.
Activation Energy	Minimum energy needed to start a reaction	Heat gives molecules activation energy.
Anhydrous	Without water	Anhydrous salts absorb moisture.

Earth Science & Geology

Word	Meaning	Example
Asthenosphere	A semi-fluid layer beneath Earth’s crust	The asthenosphere moves tectonic plates.
Atmosphere	The layer of gases around Earth	Earth’s atmosphere contains oxygen and nitrogen.
Avalanche	A large mass of snow sliding down a slope	The avalanche covered the village in snow.
Aquifer	A layer of rock that holds water	We get groundwater from aquifers.
Arid	Extremely dry, like a desert	The Sahara is an arid region.
Ascent	The act of rising or going up	The balloon made a steady ascent.
Ashfall	Volcanic ash that falls after an eruption	Ashfall covered nearby towns.
Alluvial	Related to soil or sediment from rivers	Alluvial plains are great for farming.
Atoll	A ring-shaped coral island	The Maldives are made of many atolls.
Aftershock	A smaller earthquake after a major one	The aftershock damaged already cracked buildings.

Physics & Energy

Word	Meaning	Example
Acceleration	A change in speed or direction	A car speeds up during acceleration.
Amplitude	The height of a wave	Loud sounds have a large amplitude.
Atom	The smallest particle of an element	Atoms combine to form molecules.
Angular	Related to angles or rotation	The wheel had a fast angular speed.
Attraction	A force pulling objects together	Gravity is a type of attraction.
Alternating Current	An electric current that changes direction often	Household power uses alternating current (AC).
Absorption	When a material takes in energy or light	Black clothes absorb more sunlight.
Avogadro’s Number	Number of particles in one mole (6.022×10²³)	Avogadro’s number helps count atoms.
Archimedes’ Principle	A body in water experiences an upward force	Ships float due to Archimedes’ Principle.
Antimatter	Opposite of matter, with opposite charges	Antimatter is rare in the universe.

Genetics & Molecular Biology

Word	Meaning	Example
Adenine	One of the four DNA bases	Adenine pairs with thymine in DNA.
Antibody	A protein that fights disease	Your body makes antibodies after a vaccine.
Antigen	A substance that triggers an immune response	Viruses have antigens on their surface.
Apoptosis	Programmed cell death	Apoptosis removes damaged cells.
Amino Acid	Building blocks of proteins	There are 20 amino acids in proteins.
Allele	A version of a gene	You inherit alleles from your parents.
Autosome	Any chromosome that is not a sex chromosome	Humans have 22 pairs of autosomes.
Amplification	Making more copies of a DNA section	PCR is used for DNA amplification.
Aneuploidy	A condition with extra or missing chromosomes	Down syndrome is caused by aneuploidy.
Assay	A test to measure biological activity	The lab ran an assay to test the drug.

Astronomy & Space

Word	Meaning	Example
Asteroid	A small rocky object orbiting the Sun	An asteroid belt lies between Mars and Jupiter.
Astronomy	The study of space and celestial objects	Astronomy helps us understand stars and planets.
Atmosphere	The gas layer around a planet	Earth’s atmosphere protects life.
Aurora	Lights in the sky caused by solar particles	The aurora borealis is visible in the north.
Aphelion	The point when a planet is farthest from the Sun	Earth reaches aphelion in July.
Albedo	The measure of surface reflectivity	Ice has a high albedo.
Altitude	Height above sea level or Earth’s surface	Satellites orbit at high altitudes.
Axis	An imaginary line an object rotates around	Earth spins on its axis.
Astronaut	A person trained to travel in space	Neil Armstrong was the first astronaut on the moon.
Andromeda	A nearby spiral galaxy	The Andromeda galaxy will collide with the Milky Way.

Psychology & Neuroscience

Word	Meaning	Example
Attention	The ability to focus on something	Attention is needed for learning.
Amnesia	Memory loss	He suffered amnesia after the accident.
Anxiety	A feeling of worry or fear	Anxiety affects mental health.
Association	A connection between ideas or memories	Learning is easier through association.
Aggression	Angry or violent behavior	Aggression can be a response to fear.
Adaptation	Mental or emotional adjustment to change	Moving to a new city needs adaptation.
Affect	A person’s visible emotion	He showed a flat affect after the trauma.
Attention Span	How long a person can focus	Kids have shorter attention spans.
Autonomy	Independence or control over one’s life	Autonomy is important for self-confidence.
Appraisal	Personal interpretation of a situation	Stress depends on your appraisal of danger.

Environmental Science

Word	Meaning	Example
Acid Rain	Rain that contains acidic pollutants	Acid rain damages forests and buildings.
Anthropogenic	Caused by humans	Climate change is mostly anthropogenic.
Aquatic	Related to water	Fish live in aquatic environments.
Afforestation	Planting trees where there were none before	Afforestation helps fight deforestation.
Air Pollution	Harmful substances in the air	Factories cause air pollution.
Algae Bloom	A rapid growth of algae in water	Algae blooms can harm marine life.
Abiotic Factor	A non-living environmental component	Temperature is an abiotic factor in an ecosystem.
Adaptability	The ability to adjust to changes	Animals show adaptability to climate changes.
Aquaculture	Farming fish or water organisms	Shrimp farming is a type of aquaculture.
Aerosol	Small particles in the air	Aerosols affect cloud formation and climate.

Medical Science

Word	Meaning	Example
Antibiotic	A drug used to kill bacteria	Doctors prescribe antibiotics for infections.
Anemia	A condition with low red blood cells	Fatigue can be a sign of anemia.
Analgesic	A pain-relieving medicine	Paracetamol is a common analgesic.
Antiseptic	A substance that prevents infection	Apply antiseptic on cuts.
Asthma	A disease causing breathing difficulty	Asthma attacks may need inhalers.
Amputation	Removal of a limb by surgery	The patient required leg amputation after injury.
Anesthesia	Loss of sensation used in surgery	The patient was given anesthesia before surgery.
Antiviral	A drug that fights viruses	Antiviral medicines help treat flu.
Autopsy	Examination of a body after death	An autopsy revealed the cause of death.
Arrhythmia	Irregular heartbeat	An arrhythmia may require treatment.

Computer Science

Word	Meaning	Example
Algorithm	A set of steps to solve a problem	Google uses complex algorithms for searches.
Application	A software program	I use a weather application on my phone.
API (Application Programming Interface)	A way for software to communicate with each other	The app uses an API to show maps.
Array	A list or group of data items	Arrays store multiple values in programming.
ASCII	A coding system for characters	ASCII represents letters as numbers.
Asynchronous	Processes that don’t run at the same time	Asynchronous calls don’t block other tasks.
Architecture	The structure of a computer or system	Modern computers use 64-bit architecture.
Artificial Intelligence	Machines that mimic human thinking	AI can now write stories and play games.
Authentication	Verifying a user’s identity	Passwords are used for authentication.
Access Control	Restricting who can use or see data	Firewalls provide access control for networks.

Engineering & Technology

Word	Meaning	Example
Actuator	A device that moves parts of a machine	Actuators are used in robots.
Aerodynamics	The study of how air flows over surfaces	Cars are designed with aerodynamics for speed.
Amplifier	A device that increases signal strength	Speakers have amplifiers inside.
Automation	Machines doing tasks without human help	Factories use automation to save time.
Adhesion	Sticking of one material to another	Glue helps improve adhesion.
Alloy	A mix of two or more metals	Steel is an alloy of iron and carbon.
Arch	A curved structure that supports weight	Arches are common in bridges.
Axle	A rod that connects and turns wheels	The car’s axle broke.
Aeronautics	The science of flying	Engineers study aeronautics to design airplanes.
Augmented Reality	Technology that adds digital elements to real world	AR apps can show dinosaurs in your living room.

Mathematics

Word	Meaning	Example
Angle	The space between two lines that meet at a point	A right angle is 90 degrees.
Axis	A reference line in graphs or geometry	The x-axis runs left to right.
Arithmetic	Basic number operations like addition and subtraction	Arithmetic is taught in primary school.
Algebra	Using letters to represent numbers	Algebra helps solve unknown values.
Array	A structured arrangement of numbers	Arrays are used in matrices.
Average	A number that represents a group (mean)	The average score was 80%.
Ascending Order	Sorting from smallest to largest	Sort the list in ascending order.
Approximation	A number close to the actual value	Pi is approximately 3.14.
Addition	Combining numbers to get a total	2 + 2 is an addition problem.
Axiom	A basic truth used in math logic	An axiom doesn’t need proof.

Zoology & Animal Science

Word	Meaning	Example
Amphibian	A cold-blooded animal living in water and land	Frogs are amphibians.
Arthropod	Invertebrates with jointed limbs and exoskeletons	Crabs and spiders are arthropods.
Antenna	A sensory organ found on insects	Ants use antennae to feel their surroundings.
Adaptation	A feature helping survival in an environment	A camel’s hump is an adaptation.
Asexual	Reproducing without a partner	Hydra reproduces asexually.
Altricial	Born helpless and needing care	Human babies are altricial.
Aquatic	Living in or near water	Dolphins are aquatic mammals.
Apex Predator	Top predator with no natural enemies	Lions are apex predators.
Avian	Related to birds	Eagles are avian predators.
Annelid	A type of segmented worm	Earthworms are annelids.

Conclusion

Learning these 130 science words that start with A is a smart first step toward understanding complex science topics more easily. From atom to autotroph, and from acceleration to altitude, each word builds your science vocabulary across subjects like biology, chemistry, earth science, astronomy, and psychology.

By studying these science terms starting with A, you’re creating a strong base for deeper learning. Use this science words list as part of your daily revision, flashcards, or classroom teaching Science Words That Start With A. Whether you’re a student or a lifelong learner, knowing these science words with meaning makes understanding science simpler, clearer, and much more fun Science Words That Start With A.