- Armoire
- Armour
- Armour-plated
- Aromatherapy
- Arose
- Arouse
- Aroused
- Arpanet
- Arraign
- Arrangement
- Arrayed
- Arrestable
- Articleship
- Artifice
- Artificial
- Artificial intelligence
- As opposed to
- Artificial satellite
- Artillery
- Artisan
- Artisans
- Arty
- Arum
- Aruna
- As a matter of fact
- As a rule
- As one likes
- As per
- As plain as the nose
- As pleased as punch
- As sharp as a needle
- As sure as gun
- As ugly as in
- As ugly as sin
- Asafoetida
- Ascend
- Ascended
- Ascent
- Ascertain
- Ascetic
- Ascites
- Ascorbic acid
- Asepticism
- Ash melon
- Ash-coloured
- Ash-pit
- Ashamed
- Ashtray
- Asinine
- Assemblage
- Assembly
- Assertive
- Assertively
- Assertiveness
- Assiduity
- Assiduous
- Assiduously
- Assimilate
- Assisting
- Astro
- Astrobotany
- Astrolabe
- Astrological
- Astrology
- Astronomer
- Astronomical
- Astrophysics
- Asunder
- Aswamedha
- Asylum
- Asymmetry
- At a snails pace
- At a stretch
- At a tender age
- At all events
- At dead of night
- At first
- At loggerheads
- At work
- At-the-outset
- Ataraxy
- Ataxia
- Athenaeum
- Athletic
- Atmospheric air
- Atomic power
- Attentiveness
- Attenuation
- Attested
- Atticism
- Attorney
- Attractive
- Attribution
- Aural
- Aureole
- Auricular
- Aurora australis
- Auspice
- Auspicious
- Auspicious time