The Collaborative International Dictionary of English v.0.48:

Amphibrach \Am"phi*brach\ ([a^]m"f[i^]*br[a^]k), n. [L. ?, Gr. ?
   short at both ends; 'amfi` + brachy`s short.] (Anc. Pros.)
   A foot of three syllables, the middle one long, the first and
   last short ([crescent] -- [crescent]); as, h[a^]b[=e]r[e^].
   In modern prosody the accented syllable takes the place of
   the long and the unaccented of the short; as,
   pro-phet[bprime]ic.
   [1913 Webster] Amphicarpic

WordNet (r) 3.0 (2006):

amphibrach
    n 1: a metrical unit with unstressed-stressed-unstressed
         syllables (e.g., `remember')