1. (n.) The lid of a pitcherform leaf.

2. (n.) The lid of the urnlike capsule of mosses.

3. (n.) Any lidlike or operculiform process or part; as, the opercula of a dental follicle.

4. (n.) The fold of integument, usually supported by bony plates, which protects the gills of most fishes and some amphibians; the gill cover; the gill lid.

5. (n.) The principal opercular bone in the upper and posterior part of the gill cover.

6. (n.) The lid closing the aperture of various species of shells, as the common whelk.

7. (n.) Any lid-shaped structure closing the aperture of a tube or shell.

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