- facetious 1590s, from Fr. facétieux, from facétie "a joke" (15c.), from L. facetia "jest, witticism," from facetus "witty, elegant, fine, courteous," of unknown origin, perhaps related to facis "torch." It implies a desire to be amusing, often intrusive or ill-timed. Related: Facetiously; facetiousness. "Facetiæ in booksellers' catalogues, is, like curious, a euphemism for erotica." [Fowler]
Etymology dictionary. 2014.