Lewis & Short

quā̆drĭangŭlus, a, um, adj. [quattuor-angulus], four-cornered, quadrangular (post-Aug.); figura, Plin. 13, 22, 38, § 118: herba quadriangulo caule, id. 25, 6, 27, § 63: membrum, Aus. Epigr. 128.
As subst.: quădrĭangŭlum, i, n., a quadrilateral figure, quadrangle, Prisc. Fig. Num. p. 417; cf. quadrangulum.