iambus

from WordNet (r) 3.0 (2006)

iambus
    n 1: a metrical unit with unstressed-stressed syllables [syn:
         {iamb}, {iambus}]

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]