What does "umbo" mean?

Umbo: A boss, or rounded elevation, or a corresponding depression, in a palate, disk, or membrane; as, the umbo in the integument of the larvæ of echinoderms or in the tympanic membrane of the ear.

Additional senses

  1. 2.(Zoöl.) One of the lateral prominence just above the hinge of a bivalve shell.

Sources