- authenticity: The state or quality of being genuine, or of the origin and authorship claimed.
- autobiography: The story of one's life written by himself.
- autocracy: Absolute government.
- autocrat: Any one who claims or wields unrestricted or undisputed authority or influence.
- automaton: Any living being whose actions are or appear to be involuntary or mechanical.
- autonomous: Self-governing.
- autonomy: Self-government.
- autopsy: The examination of a dead body by dissection to ascertain the cause of death.
- autumnal: Of or pertaining to autumn.
- auxiliary: One who or that which aids or helps, especially when regarded as subsidiary or accessory.
- avalanche: The fall or sliding of a mass of snow or ice down a mountain-slope, often bearing with it rock.
- avarice: Passion for getting and keeping riches.
- aver: To assert as a fact.
- averse: Reluctant.
- aversion: A mental condition of fixed opposition to or dislike of some particular thing.
- avert: To turn away or aside.
- aviary: A spacious cage or enclosure in which live birds are kept.
- avidity: Greediness.
- avocation: Diversion.
- avow: To declare openly.
- awaken: To arouse, as emotion, interest, or the like.
- awry: & adj. Out of the proper form, direction, or position.
- aye: An expression of assent.
- azalea: A flowering shrub.
- azure: The color of the sky.
- Baconian: Of or pertaining to Lord Bacon or his system of philosophy.
- bacterium: A microbe.
- badger: To pester.
- baffle: To foil or frustrate.
- bailiff: An officer of court having custody of prisoners under arraignment.
- baize: A single-colored napped woolen fabric used for table-covers, curtains, etc.
- bale: A large package prepared for transportation or storage.
- baleful: Malignant.
- ballad: Any popular narrative poem, often with epic subject and usually in lyric form.
- balsam: A medical preparation, aromatic and oily, used for healing.
- banal: Commonplace.
- barcarole: A boat-song of Venetian gondoliers.
- baritone: Having a register higher than bass and lower than tenor.
- barograph: An instrument that registers graphically and continuously the atmospheric pressure.
- barometer: An instrument for indicating the atmospheric pressure per unit of surface.
- barring prep: Apart from.
- bask: To make warm by genial heat.
- bass: Low in tone or compass.
- baste: To cover with melted fat, gravy, while cooking.
- baton: An official staff borne either as a weapon or as an emblem of authority or privilege.
- battalion: A body of infantry composed of two or more companies, forming a part of a regiment.
- batten: A narrow strip of wood.
- batter: A thick liquid mixture of two or more materials beaten together, to be used in cookery.
- bauble: A trinket.
- bawl: To proclaim by outcry.