- aspirant: One who seeks earnestly, as for advancement, honors, place.
- aspiration: An earnest wish for that which is above one's present reach.
- aspire: To have an earnest desire, wish, or longing, as for something high and good, not yet attained.
- assailant: One who attacks.
- assassin: One who kills, or tries to kill, treacherously or secretly.
- assassinate: To kill, as by surprise or secret assault, especially the killing of some eminent person.
- assassination: Murderer, as by secret assault or treachery.
- assay: The chemical analysis or testing of an alloy ore.
- assent: To express agreement with a statement or matter of opinion.
- assess: To determine the amount of (a tax or other sum to be paid).
- assessor: An officer whose duty it is to assess taxes.
- assets: pl. Property in general, regarded as applicable to the payment of debts.
- assiduous: Diligent.
- assignee: One who is appointed to act for another in the management of certain property and interests.
- assimilate: To adapt.
- assonance: Resemblance or correspondence in sound.
- assonant: Having resemblance of sound.
- assonate: To accord in sound, especially vowel sound.
- assuage: To cause to be less harsh, violent, or severe, as excitement, appetite, pain, or disease.
- astringent: Harsh in disposition or character.
- astute: Keen in discernment.
- atheism: The denial of the existence of God.
- athirst: Wanting water.
- athwart: From side to side.
- atomizer: An apparatus for reducing a liquid to a fine spray, as for disinfection, inhalation, etc.
- atone: To make amends for.
- atonement: Amends, reparation, or expiation made from wrong or injury.
- atrocious: Outrageously or wantonly wicked, criminal, vile, or cruel.
- atrocity: Great cruelty or reckless wickedness.
- attache: A subordinate member of a diplomatic embassy.
- attest: To certify as accurate, genuine, or true.
- attorney-general: The chief law-officer of a government.
- auburn: Reddish-brown, said usually of the hair.
- audacious: Fearless.
- audible: Loud enough to be heard.
- audition: The act or sensation of hearing.
- auditory: Of or pertaining to hearing or the organs or sense of hearing.
- augment: To make bigger.
- augur: To predict.
- Augustinian: Pertaining to St. Augustine, his doctrines, or the religious orders called after him.
- aura: Pervasive psychic influence supposed to emanate from persons
- aural: Of or pertaining to the ear.
- auricle: One of the two chambers of the heart which receives the blood from the veins.
- auricular: Of or pertaining to the ear, its auricle, or the sense of hearing.
- auriferous: Containing gold.
- aurora: A luminous phenomenon in the upper regions of the atmosphere.
- auspice: favoring, protecting, or propitious influence or guidance.
- austere: Severely simple; unadorned.
- autarchy: Unrestricted power.
- authentic: Of undisputed origin.