- Arid
- Arise
- Arisen
- Aristocracy
- Arithmetic
- Arithmetic progression
- Arithmetical progression
- Armada
- Armadillo
- Armature
- Armchair
- Armed
- Armed neutrality
- Armenius
- Armhole
- Armoire
- Armour
- Armour-plated
- Aromatherapy
- Arose
- Arouse
- Aroused
- Arpanet
- Arraign
- Arrangement
- Arrayed
- Arrestable
- Arrogant person
- Arrogantly
- Arrow-root plant
- Arrowhead
- Arrowroot
- Arsenal
- Arsonist
- Art of war
- Artefact
- Artful
- Article
- 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 common as much
- As common as muck
- As cool as a cucumber
- As far as
- As far as i know
- As far as one can tell
- As far as one is concerned
- As flat as a pancake
- As for
- As good as new
- As long as
- As many again
- 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
- Askew
- Asocial
- Asp
- Asparagus
- Aspect
- Asperity
- Aspersions
- Asphodel
- Asphyxiate
- Assamese
- Assassination
- Assaulting
- Assemblage