n. [ Gr. &unr_;; &unr_; shell + e'i^dos form: cf. F. conchoïde. ] (Geom.) A curve, of the fourth degree, first made use of by the Greek geometer, Nicomedes, who invented it for the purpose of trisecting an angle and duplicating the cube. [ 1913 Webster ]

a. [ Cf. F. conchoïdal. ] (Min.) Having elevations or depressions in form like one half of a bivalve shell; -- applied principally to a surface produced by fracture. [ 1913 Webster ]