Source : Webster's Revised Unabridged Dictionary (1913)

Iamb \I"amb\, n. [Cf. F. iambe. See {Lambus}.]
   An iambus or iambic. [R.]

Source : WordNet®

iamb
     n : a metrical unit with unstressed-stressed syllables [syn: {iambus}]
     [also: {iambi} (pl)]