tribrach

noun

tri·​brach ˈtrī-ˌbrak 

: a metrical foot of three short syllables of which two belong to the thesis and one to the arsis

tribrachic

trī-ˈbra-kik 

adjective

Word History

Etymology

Latin tribrachys, from Greek, having three short syllables, from tri- + brachys short — more at brief

First Known Use

1589, in the meaning defined above