a. and sb. Geom. [ad. Gr. τριγωνοειδής of triangular form: see TRIGON and -OID.] a. adj. Resembling a triangle; approximately triangular. b. sb. A plane figare contained by three circular arcs of equal radius meeting at angles; a species of curvilinear triangle. So Trigonoidal a., (a) Nat. Hist. = trigonoid adj.; (b) Geom. ‘like a trigonoid’ (Cent. Dict., 1891).
1822. J. Parkinson, Outl. Oryctol., 217. Subcordated, trigonoidal.
1873. Salmon, Higher Plane Curves, 245. The quartic is a triacnodal curve composed of a trigonoid figure within the triangle and of the three vertices as acnodes.
