Source : Webster's Revised Unabridged Dictionary (1913)

Iambus \I*am"bus\, n.; pl. L. {Iambi}, E. {Iambuses}. [L.
   iambus, Gr. ?; prob. akin to ? to throw, assail (the iambus
   being first used in satiric poetry), and to L. jacere to
   throw. Cf. {Jet} a shooting forth.] (Pros.)
   A foot consisting of a short syllable followed by a long one,
   as in [a^]m[=a]ns, or of an unaccented syllable followed by
   an accented one, as invent; an iambic. See the Couplet under
   {Iambic}, n.

Source : WordNet®

iambus
     n : a metrical unit with unstressed-stressed syllables [syn: {iamb}]