Why is the ninth month called September?
1590s, from French facétieux, from facétie "a joke" (15c.), from Latin 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]