Discoid

Part of speech: noun (n.)

Anything having the form of a discus or disk; particularly, a discoid shell.

Part of speech: adjective (a.)

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. 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.