| Term | Definition |
| anthropology | The science of man in general. |
| anthropomorphous | Having or resembling human form. |
| antic | A grotesque, ludicrous, or fantastic action. |
| Antichrist | Any opponent or enemy of Christ, whether a person or a power. |
| anticlimax | A gradual or sudden decrease in the importance or impressiveness of what is said. |
| anticyclone | An atmospheric condition of high central pressure, with currents flowing outward. |
| antidote | Anything that will counteract or remove the effects of poison, disease, or the like. |
| antilogy | Inconsistency or contradiction in terms or ideas. |
| antipathize | To show or feel a feeling of antagonism, aversion, or dislike. |
| antiphon | A response or alteration of responses, generally musical. |
| antiphony | An anthem or other composition sung responsively. |
| antipodes | A place or region on the opposite side of the earth. |
| antiquary | One who collects and examines old things, as coins, books, medals, weapons, etc. |
| antiquate | To make old or out of date. |
| antique | Pertaining to ancient times. |
| antiseptic | Anything that destroys or restrains the growth of putrefactive micro-organisms. |
| antislavery | Opposed to human slavery. |
| antispasmodic | Tending to prevent or relieve non-inflammatory spasmodic affections. |
| antistrophe | The inversion of terms in successive classes, as in "the home of joy and the joy of home". |
| antitoxin | A substance which neutralizes the poisonous products of micro-organisms. |
| antonym | A word directly opposed to another in meaning. |
| anxious | Distressed in mind respecting some uncertain matter. |
| apathy | Insensibility to emotion or passionate feeling. |
| aperture | Hole. |
| apex | The highest point, as of a mountain. |
| aphorism | Proverb. |
| apiary | A place where bees are kept. |
| apogee | The climax. |
| apology | A disclaimer of intentional error or offense. |
| apostasy | A total departure from one's faith or religion. |
| apostate | False. |
| apostle | Any messenger commissioned by or as by divine authority. |
| apothecary | One who keeps drugs for sale and puts up prescriptions. |
| apotheosis | Deification. |
| appall | To fill with dismay or horror. |
| apparent | Easily understood. |
| apparition | Ghost. |
| appease | To soothe by quieting anger or indignation. |
| appellate | Capable of being appealed to. |
| appellation | The name or title by which a particular person, class, or thing is called. |
| append | To add or attach, as something accessory, subordinate, or supplementary. |
| appertain | To belong, as by right, fitness, association, classification, possession, or natural relation. |
| apposite | Appropriate. |
| apposition | The act of placing side by side, together, or in contact. |
| appraise | To estimate the money value of. |
| appreciable | Capable of being discerned by the senses or intellect. |
| apprehend | To make a prisoner of (a person) in the name of the law. |
| apprehensible | Capable of being conceived. |
| approbation | Sanction. |
| appropriate | Suitable for the purpose and circumstances. |