- Arboretum
- Arcane
- Arch-rival
- Archaeologist
- Archbishop
- Archery
- Architecturally
- Arian
- Aries
- Aristocrat
- Aristocratic
- Arithmetical
- Armed guard
- Armed to the teeth
- Armistice
- Arrow-tip
- Art of arms
- Art of dancing
- Art paper
- Artefactual
- Artery
- Arthritis
- Artichoke
- Artichokes
- As free as air
- As helpless as a babe
- As i see it
- As it comes
- As it stands
- As keen as mustard
- As large as life
- As many
- As matter of
- As much as possible
- As of
- Ascending
- Ascending node of caput draconis
- Ascii
- Ascription
- Aseity
- Asepsis
- Ash
- Ash wednesday
- Ash-gourd
- Ask for a blank cheque
- Ask for the moon
- Assembling
- Assertion
- Assessment
- Assets
- Assignation
- Assignee
- Assimilation
- Assist in
- Associates
- Association
- Astrogeology
- Astroid
- Astrologers
- Astronaut
- Astrophysicist
- Asvamedha sacrifice
- Asymmetrical
- Asymptote
- At a loose end
- At a price
- At a run
- At one leisure
- At one's fingertips
- At ones last gasp
- At ones own pace
- At that
- Atomic theory
- Atomic warfare
- Atomic weight
- Atoms
- Atomy
- Atony
- Atriculate
- Attach
- Attack
- Attacked
- Attained puberty
- Aubade
- Auberage
- Aubergine
- Aubum hair
- Auction
- Auctionary
- Audience
- Audio
- Audio-visual aids
- Auditory ossicles
- Augean stables
- Augmentation
- Augur
- Augury
- Authoritatively
- Authority
- Authorization