Lie; falsehood; fib; untruth; mendacity.
Lie---harsh and direct, everyday word for a statement which distorts or suppresses truth.
Falsehood---more dignified and less offensive term.
Fib---not slang but standard English [from FABLE]; a trivial falsehood, uttered with good intentions.
Untruth---less reprehensible than a falsehood; a statement either intentionally misleading, or so, due to misunderstanding or ignorance.
Mendacity---disposition to lie, perhaps habitually.
A DICTIONARY OF CONTEMPORARY AMERICAN USAGE, 1957, by Bergen Evans and Cornelia Evans, p. 274.