Main Entry: oper·cu·lum

Pronunciation: \ō-ˈpər-kyə-ləm\

Function: noun

Inflected Form(s): plural oper·cu·la \-lə\ also oper·cu·lums

Etymology: New Latin, from Latin, cover, from operire to shut, cover

Date: 1681

1 : a body process or part that suggests a lid: as a : a horny or shelly plate on the posterior dorsal surface of the foot in many gastropod mollusks that closes the shell when the animal is retracted b : the covering of the gills of a fish — see fish illustration
2 : a lid or covering flap (as of a moss capsule)