- Acoustics
- Acquaintances
- Act up to
- Acting
- Actinic
- Actinotherapy
- Action plan
- Actions
- Actions speak louder than words
- Activation
- Active and passive voices
- Activex
- Add to
- Addenda
- Additionally
- Address size
- Adenoids
- Adept
- Adequacy
- Administratively
- Administrator
- Admirably
- Admiralty
- Admire for
- Admired
- Admissible
- Admittedly
- Admix
- Admonish
- Adolescence
- Adopted
- Adorable
- Adoration
- Adventurer
- Adventures
- Adventurous
- Adversarial
- Adversity
- Advertise
- Advisors
- Advocacy
- Adze
- Aegis
- Aeon
- Aeration
- Affectionately
- Affinity with (for, between)
- Affix
- Affluenza
- Affright
- Affront
- Affronted by
- Afterthought
- Again
- Against the grain
- Against the hair
- Agamas
- Agate
- Age
- Age of shams
- Aged bull
- Ageism
- Agency
- Agent
- Ages
- Agglutinate
- Airsickness
- Agreed
- Agriculturist
- Agro
- Agroforestry
- Ahalya
- Ahead of
- Ahem
- Ai
- Aid
- Aide
- Aids
- Aileron
- Ailment
- Aimed
- Aimlessly
- Aimlessness
- Airspace
- Airway
- Airwoman
- Airworthiness
- Aka
- Akaru
- Alabama
- Alamode
- Alarmingly
- Alarmist
- Alignment
- Alimony
- Alive and kicking
- Alkali ash
- All -in
- All and sundry
- All around