umbo

noun pl. um·bo′·nesum bō′nēz or um′·bos

1. the boss, or knob, at the center of a shield
2. something resembling this; specif.,
   1. the elevation beside the hinge on each half of a bivalve shell
   2. the prominence on the eardrum at the point of attachment of the malleus

Etymology: L, akin to umbilicus, navel