Triangulus, triáoguli, m. g. pen. cor. Ci. A triangle: a figure that hath three cornets.Triangulus ager. Col. A three cornerd ficld.
Lewis and Short: Latin dictionary
trĭangŭlus, a, um, adj. [tres-angulus], having three corners or angles, threecornered, triangular.I.Adj.: sidera, Cic. Div. 2, 42, 89: forma cutis, Cels. 7, 25, 2: species (Siciliae), Plin. 3, 8, 14, 86: ager, Col. 5, 2, 5: latera radicis, id. 13, 11, 218 et saep.—II.Substt.a. trĭangŭlum, i, n., a triangle: quadrata amplius spatium complectuntur triangulis, Quint. 1, 10, 41; so id. 1, 10, 3; Cic. N. D. 2, 49, 125; Plin. 27, 8, 39, 61.—b. trĭangŭlus, i, m., a triangle, Front. Expos. Form. pp. 32, 33, 35 Goes.