- Aplasia
- Aplenty
- Apocalyptic
- Apolitical
- Apologue
- Apoplectic
- Apostatize
- Apostrophe
- Apotheosis
- Applicable
- Application window
- Applicator
- Appointed
- Appointed time
- Apposite
- Apposition
- Appraisal
- Appraised
- Appreciation
- Aptitude
- Aptness
- Aqua
- Aquamarine
- Aquaphobia
- Aquarius
- Aquatic
- Aqueous
- Aquifer
- Arabia
- Arabic
- Arak
- Arbitrary
- Arbor
- Arcot
- Arcturus
- Are
- Area code
- Arena
- Areola
- Argania
- Argon
- 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
- Association of ideas
- Assurance
- Assuredly
- Astern
- Astonish
- Astonishing
- Astonishingly
- Astounded
- Astounding
- Astraphobia
- Astride
- At a stroke
- At all
- At any cost
- At any moment
- At every turn
- At first light
- At first sight
- At great length
- At least
- At most
- At night
- At odds
- At this rate
- At time
- At war
- Atavism
- Ate