One Words Letter - A

adult = a person who has grown to full size and strength; a person above eighteen years of age.

adulterate = to make impure or poorer in quality by adding something of less value; to add water to (Milk).
adulteress = a married woman who has had voluntary sexual intercourse with a man who is not her husband.
alien = a person residing in a country of which he is not a citizen.
ambiguous = of doubtful meaning; of double meaning.
amateur = person who paints pictures, performs music, plays, etc, for the love of it, not for money.

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amnesty = general pardon for offences against the state.
anarchy = absence of government; absence of control.
anachronism = something out of date now or in a description of past events 
annual = happening every year.
anonymous = without a name, or with a name that is not made known; (a letter) that does not bear the name of the writer.
annuity = fixed sum of money paid to somebody yearly as income during his lifetime.
anodyne = medicine or drug that brings down pain.
antagonize = to make an enemy of.
antecedents = past history of a person or persons. 
antedate = to put an earlier date on (a letter, document etc.)
antiseptic = substance that prevents the growth of bacteria; substance that prevents putrefaction.
antidote = medicine used against a poison; medicine that counteracts the effect of a poison or drug.
antiquary = person who studies, collects, or sells, antiquities.
antiquarian = connected with the study of antiquities; person who studies, collects, or sells, antiquities.
anti-personnel = (of bombs, mines etc) designed to kill or wound human beings (not to destroy buildings)
antonym = word that is contrary in meaning, opposite word.
amphibian = animal able to live both on land and in water.

applause = loud approval or praise, loud clapping of hands; clapping and cheering.
aquatic = (of plants, animals etc.) growing or living in or near water; (of sports) taking place on or in water.
arbitrary = based on opinion or impulse only, not on reason.
arbitrate = to judge between two parties to a dispute.
arbitrator = person appointed by two parties to settle a dispute.
archaeology = study of ancient things, especially remains of pre-historic times

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archaic = (of words, language, etc.) not now used except for special purposes; of ancient times.
archipelago = (sea with a) group of small islands.
architect = person who draws plans for buildings and looks after the work of building.
architecture = art and science of building; design and style of buildings.
aristocracy = government by persons of the highest social rank; ruling body of nobles; the social class from which these nobles come.
aristocrat = member of the class of nobles; person of noble birth.
armada = great fleet of warships.
armour = defensive covering, usually metal, for the body, worn in fighting.
artificial = not natural or real, made by the art of man.
artiste = professional singer, actor, dancer etc.
ascent = to go or come up.
ascent = going up, upward movement.
ascetic = person who leads a severely simple life without ordinary pleasures; one who practises self-denial and self discipline.
astronaut = a person trained for space flight.
astronomy = science of the heavenly bodies; science of the sun, moon, stars and planets.
astride = with one leg on each side (of)
astray = away from the right path.
atheist = one who believes that there is no God.
autobiography= the history of a man’s life written by himself.
autocracy = government by a ruler who has unlimited power.
aversion = strong dislike.
aviary = place for keeping birds.
aviation = (art and science of) flying in aircraft.
avoid = fight shy; keep away from.