Definition of rostellum:
(n) :
(biology) A 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.
(n) :
(botany) A projecting part of the column in the flower of an orchid that separates the male stamen from the female gynoecium.
(n) :
A small beak-like process or extension; a small rostrum.