coolth (n.)youdaoicibaDictYouDict
1540s, from cool on the model of warmth. It persists, and was used by Pound, Tolkien, Kipling, etc., but it never has shaken its odor of facetiousness and become standard.
facetious (adj.)youdaoicibaDictYouDict
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, amusing," 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]