- addiction (to grab advantage)
- addiction to intoxicants. consuming alcohol as an addiction
- american harvest mouse
- american grey birch
- Arrhenatherum
- Alpinia
- Aeonium
- Aframomum
- Agrostis
- Arenga
- alula
- aftershaft
- armored dinosaur
- agglutinable
- agglutinating activity
- agglutinative
- agglutination reaction
- agglutination test
- arch of aorta
- angioma serpiginosum
- arch way
- angiopathy
- antisepsis
- autoregulation
- anovulation
- assimilation
- Acacia melanoxylon
- apheresis
- afibrinogenemia
- alkalemia
- acanthocytosis
- agranulosis
- agranulocytosis
- analbuminemia
- anorexic
- anorectic
- anadromous
- Anguillula
- Ascaris
- Ascaridia
- apoplectoid
- articles on approval
- articles of apparel
- articles (of association etc. of a company)
- article of commerce
- apron stage
- arm folding
- apriori
- apron strings
- accra