c. 1300, "deceitfulness, treachery, dishonesty," from Old French fauseté "falsehood" (12c., Modern French fausseté), from Late Latin falsitatem (nominative falsitas), from Latin falsus "erroneous, mistaken" (see false). From late 14c. as "untrue statement or doctrine;" from 1570s as "character of being not true."
