Source : Webster's Revised Unabridged Dictionary (1913)

Conchoid \Con"choid\, n. [Gr. ?; ? shell + ? form: cf. F.
   concho["i]de.] (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.