- Alexandrian
- abyssal zone
- albatross
- adolph simon ochs
- Argonauta argo
- Argonaut
- acrocephaly
- aboriginal
- alimental
- Aplodontia rufa
- agouti
- abrocome
- artificial skin
- answering machine
- atrioventricular bundle
- atrioventricular node
- atrioventricular trunk
- anteater
- aquatic mammal
- aardvark
- ant bear
- aplacental
- African elephant
- Albers_Schonberg disease
- abetalipoproteinemia
- allegheny spurge
- allegheny mountain spurge
- abies amabilis
- acipenser transmontanus
- appeasement
- appease
- assuage
- andante
- accelerando
- allegretto
- aggrandize
- aggrandise
- agony
- ail
- acetanilid
- aspirin
- acetphenetidin
- acetanilide
- acetophenetidin
- aminopyrine
- acetylsalicylic acid
- Anacin III
- acetaminophen
- amidopyrine
- atrocious