- 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 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
- Askew
- Asocial
- Asp
- Asparagus
- Aspect
- Asperity
- Aspersions
- Asphodel
- Asphyxiate
- Assamese
- Assassination
- Assaulting
- Assemblage
- Assembly
- Assertive
- Assertively
- Assertiveness
- Assiduity
- Assiduous
- Assiduously
- Assimilate
- Assisting
- At a stretch
- At a tender age
- At all events
- At dead of night
- At first
- At loggerheads
- At peace
- At rest
- At school
- At the drop of a hat
- At the end of the tether
- At the full
- At the sea
- At the wicket
- Atomizer
- Atrium
- Atrocity
- Attache