- argonautidae
- asphodelaceae
- azollaceae
- athyriaceae
- audibleness
- absorptive spectrum
- arguer
- argument for argument's sake
- Accipiter cooperii
- Accipiter gentilis
- a suffix appended to nouns to impart the meaning of one who does
- Armenian Church
- Armenian Apostolic Orthodox Church
- Asian shamanism
- as good as word
- a man of god
- a lump in ones throat
- ammonia water
- ammonium hydroxide
- alphanumeric display
- active matrix screen
- arroba
- asea
- antidorcas euchore
- antidorcas marsupialis
- Alpine mouse_ear
- Astrantia major
- Arctic mouse_ear
- analgesic antagonist
- analgesia dolorosa
- analgesic action
- analgetic
- analgesic hypnotic
- anticlockwise hair whorl
- Atabrine
- active placebo
- antispasmodic enema
- aperea
- amethopterin
- atorvastatin
- antipypnotic
- amiodarone
- anticytoplasmic antibody
- antimalarial
- antimalarial drug
- astringent enema
- antiarrhythmic agent
- aminophylline
- Alupent
- Atrovent