1610s, "poem in ithyphallic meter," from Greek ithyphallos "phallos carried in the festivals," from ithys "straight" + phallos "erect penis" (see phallus). As an adjective from 1795. The meter was that of the Bacchic hymns, which were sung in the rites during which such phalloses were carried. Thus, in Victorian times, the word also meant "grossly indecent" (1864).