n. In the spicular elements of the hexactinellid sponges, a straight shaft or rhabd with rays at one end grouped together in the form of an umbel.n. An inflorescence consisting of a number of flower-stalks or pedicels, nearly equal in length, spreading from a common center, their summits forming a level, convex, or even globose surface, more rarely a concave one, as in the carrot. See cuts under inflorescence, Thapsia, and Œnanthe.n. In zoology, an umbelliform tuft, cluster, or group of parts, as of polypites borne upon a polypidom. See cut under Umbellularia.