faux (adj.)

late Old English, "intentionally untrue, lying," of religion, "not of the true faith, not in accord with Christian doctrines," from Old French fals, faus "false, fake; incorrect, mistaken; treacherous, deceitful" (12c., Modern French faux), from Latin falsus "deceptive, feigned, deceitful, pretend," also "deceived, erroneous, mistaken," past participle of fallere "deceive, disappoint," which is of uncertain origin (see fail (v.)).

From c. 1200 as "deceitful, disloyal, treacherous; not genuine;" from early 14c. as "contrary to fact or reason, erroneous, wrong." Adopted into other Germanic languages (cognates: German falsch, Dutch valsch, Old Frisian falsk, Danish falsk), though in English alone does the active sense of "deceitful" (a secondary sense in Latin) predominate.

False alarm recorded from 1570s. False step (1700) translates French faux pas. To bear false witness is attested from mid-13c. False prophet "one who prophecies without divine commission or by evil spirits," is attested from late 13c. The sporting contest false start is attested by 1850.