- pentagon
- plane figure with five angles and five sides, 1570, from M.Fr. pentagone, from L.L. pentagonum "pentagon," from Gk. pentagonon, properly neut. of adj. pentagonos "five-angled," from pente "five" + gonia "angle" (see knee). The U.S. military headquarters Pentagon was completed 1942, so called for its shape; used allusively for "U.S. military leadership" from 1945.