The Collaborative International Dictionary of English v.0.48:
dibrach \dibrach\ n. (Prosody) a foot of two short (unstressed-unstressed) syllables. Syn: pyrrhic. [WordNet 1.5]WordNet (r) 3.0 (2006):
dibrach n 1: a metrical unit with unstressed-unstressed syllables [syn: pyrrhic, dibrach]