From The Collaborative International Dictionary of English v.0.48:
Falsity \Fal"si*ty\, n.;pl. Falsities. [L. falsitas: cf. F.
fausset['e], OF. also, falsit['e]. See False, a.]
1. The quality of being false; coutrariety or want of
conformity to truth.
[1913 Webster]
Probability does not make any alteration, either in
the truth or falsity of things. --South.
[1913 Webster]
2. That which is false; falsehood; a lie; a false assertion.
[1913 Webster]
Men often swallow falsities for truths. --Sir T.
Brown.
Syn: Falsehood; lie; deceit.
Usage: Falsity, Falsehood, Lie. Falsity denotes the
state or quality of being false. A falsehood is a
false declaration designedly made. A lie is a gross,
unblushing falsehood. The falsity of a person's
assertion may be proved by the evidence of others and
thus the charge of falsehood be fastened upon him.
[1913 Webster]