- a singer and dancer (in a derogatory sense)
- a deep note
- annual
- a living dog is better than a dead lion
- adoptive mother
- aeschynanthus
- aerophilous
- acrodotism
- aquatic
- aerobatic
- aerophilic
- aerobic organism
- aerobic heat
- aerobic respiration
- animal leg
- animal inoculation
- acrodermatitis
- acellular slime mold
- ascomycetes
- Astreus pteridis
- Astreus hygrometricus
- a word evolved indigenously
- ascolis thermoprecipitin reaction
- amphicone
- academic actions
- acheson
- a sub_judge
- an inexperienced person
- atelinae
- ateliotic
- a mother who begets a brave
- an abandoner
- accousticophobia
- all hell was let loose
- a small tank
- a column built to commemorate a triumphal event
- atrophic scirrhous carcinoma
- astir
- anisoploid
- affront
- affuse
- apparent shortening
- anticlinal wall
- as closely as possible
- as clear as a bell
- anon.
- a smile
- abloom
- anonymous donation
- anonymous mycobacterium