A tribrach is a metrical foot used in formal poetry and Greek and Latin verse. In quantitative meter (such as the meter of classical verse), it consists of three short syllables; in accentual-syllabic verse (such as formal English verse), the tribrach consists of three stressed syllables.
In surveying science, a tribrach means an instrument attachment plate containing three thumbscrews (see theodolite). The device consists of two triangular metal plates, which are connected at their corners by thumbscrews. By turning these, it is possible to level the top plate, when the bottom plate has been mounted atop a tripod.