in the Greek and Latin prosody, a poetical foot, consisting of a short syllable followed by a long one; as in

"Syllaba longa brevi subjecta vocatur iambus," as Horace expresses it; and he also calls the iambus a swift, rapid foot, pes citus.

The word, according to some, took its rise from Iambus, the son of Pan and Echo, who invented this foot; or, perhaps, who only used sharp, biting expressions to Ceres, when afflicted for the death of Proserpine. Others derive it from the Greek ἱπτιον, poison, poison; or from λαγκευον, maleficium, I rail or revile, because the verses composed of iambuses were at first used only in satire.