1.NounA small beak-like process or extension; a small rostrum.
"the rostellum of the stigma of violets, or of the operculum of many mosses"
2.NounA projecting part of the column in the flower of an orchid that separates the male stamen from the female gynoecium.
3.NounA retractable protruding part at the anterior end of a soft-bodied tapeworm; the scolex from which it protrudes is often armed with hooks which serve to keep it in place attached to the host.