- anisotropy
- agora
- activist
- akaryote
- atomizer
- Apostle
- apraxia
- amongst
- atop
- aluminum foil
- androgenic
- asteroid
- argus pheasant
- apogee
- atherosclerosis
- acropolis
- applied psychology
- aestivate
- adiabatic process
- atomic power
- absorption band
- atomic mass
- atomic weight
- apoenzyme
- amyloid
- annunciator
- austral
- anthozoa
- aural
- and then
- aldebaran
- according
- arcuate
- aortic arch
- adipose cell
- arrack
- acrocentric
- angler
- accommodative
- asunder
- annular eclipse
- Addressograph
- air sac
- Assyriology
- arching
- adulterant
- amnesiac
- actinic dermatitis
- adsorbate
- associative