discoid

a. [ Gr. &unr_; quoit-shaped, &unr_; a round plate, quoit + e'i^dos form, shape: cf. F. discoïde. See Disk. ] Having the form of a disk, as those univalve shells which have the whorls in one plane, so as to form a disk, as the pearly nautilus. [ 1913 Webster ]

Discoid flower (Bot.), a compound flower, consisting of tubular florets only, as a tansy, lacking the rays which are seen in the daisy and sunflower. [ 1913 Webster ]

n. Anything having the form of a discus or disk; particularly, a discoid shell. [ 1913 Webster ]