operculum

noun5

1. •
   A covering flap in animals and insects, such as a gill cover or the lid of nits.

   • Hyoliths […] have a small, conical calcium carbonate shell, with a lid called an operculum. — 2017
2. •
   The lidlike portion of a moss sporangium or of a fruit that detaches to allow the dispersal of spores or seeds.
3. •
   A gum flap covering (part of) a partially erupted tooth, usually a wisdom tooth.
4. •
   A structure which serves as a cover or lid.

   • I lifted the circular operculum from its place and laid it carefully on the bale. — 1900
5. •
   One of several flaps of cerebral cortex covering the insula.