fraudulent (adj.)

mid-14c., "criminal deception" (mid-13c. in Anglo-Latin); from Old French fraude "deception, fraud" (13c.), from Latin fraudem (nominative fraus) "a cheating, deceit," of persons "a cheater, deceiver," of uncertain origin. Connections have been proposed to Sanskrit dhruti- "deception; error."

Meaning "a fraudulent production, something intended to deceive" is from 1650s. The meaning "impostor, deceiver, pretender; humbug" is attested from 1850. Pious fraud (1560s) is properly "deception practiced for the sake of what is deemed a good purpose;" colloquially used as "person who talks piously but is not pious at heart."