"expelling or having the quality of expelling flatulence," early 15c., from Latin carminativus, from past participle stem of carminare "to card," from carmen, genitive carminis, "a card for wool or flax," which is related to carrere "to card" (see card (v.2).
A medical term from the old theory of humours. The object of carminatives is to expel wind, but the theory is that they dilute and relax the gross humours from whence the wind arises, combing them out like knots in wool. [Hensleigh Wedgwood, "A Dictionary of English Etymology," 1859]
As a noun from 1670s.