"sportive, playful," 1590s, from French facétieux (16c.), from facétie "a joke" (15c.), from Latin facetiae "jests, witticisms" (singular facetia), from facetus "witty, elegant, fine, courteous," which is of unknown origin, perhaps related to facis "torch."
Formerly often in a good sense, "witty, full of fun, amusing," as Century Dictionary (1897) has it, "jocular, without lack of dignity;" but later implying a desire to be amusing that is often intrusive or ill-timed. Related: Facetiously; facetiousness.
Facetiæ in booksellers' catalogues, is, like
curious, a euphemism for erotica. [Fowler]