operculum (n.)

"a lid or cover; an organic structure like a lid, flap, or cover," 1713, from Latin operculum "cover, lid," from operire "to cover, close," from PIE compound *op-wer-yo-, from *op- "over" (see epi-) + root *wer- (4) "to cover." With instrumental suffix *-tlom. Related: Opercular.