| Term | Definition |
| abandon | total lack of inhibition |
| abate | to decrease, to reduce |
| abet | to aid; to act as an accomplice |
| abjure | to renounce under oath; to abandon |
| abnegate | to give up; to deny to oneself |
| abortive | ending without results |
| abrogate | to annul; to abolish by authoritative action |
| abscond | to leave quickly in secret |
| abstemious | done sparingly; consuming in moderation |
| accede | to express approval; to agree to |
| acclivity | an incline or upward slope, the ascending side of a hill |
| accretion | a growth in size; an increase in amount |
| acme | the highest level or degree attainable |
| actuate | to put into motion, to activate; to motivate or influence to activity |
| acuity | sharp vision or perception characterized by the ability to resolve fine detail |
| acumen | sharpness of insight, mind, and understanding; shrewd judgement |
| adamant | stubbornly unyielding |
| adept | extremely skilled |
| adjudicate | to hear and settle a manner; to act as a judge |
| adjure | to appeal to |
| admonish | to caution or warn gently in order to correct something |
| adroit | skillful; accomplished; highly competent |
| adulation | excessive flattery or admiration |
| adumbrate | to give a hint or indication of something to come |
| aerie | a nest high in the air; an elevated, often secluded, dwelling |