- authorization
- authorize
- autistic
- autoclave
- autogenesis
- autogenous
- autograph
- autolatry
- automated
- automatic pistol
- automatic pilot
- automotive vehicle
- autonomous
- autonomy
- autoplasty
- autopsy
- autosome
- auxiliary verb
- auxiliary storage
- avail
- avalanche
- avarice
- activated charcoal
- adamant
- airspeed
- air current
- amplify
- assembly program
- application
- annotation
- abdominal wall
- abdomen
- alto
- animalcule
- aerobe
- animal
- accomplished
- ascetic
- amine
- annihilate
- ambulance
- adjure
- archer
- analyst
- amusement
- alcoholism
- adjustment
- atomic clock
- addict
- athlete