from
The Collaborative International Dictionary of English v.0.48
Operculum \O*per"cu*lum\, n.; pl. L. {Opercula}, E.
{Operculums}. [L., a cover or lid, fr. operire to cover.]
1. (Bot.)
(a) The lid of a pitcherform leaf.
(b) The lid of the urnlike capsule of mosses.
[1913 Webster]
2. (Anat.)
(a) Any lidlike or operculiform process or part; as, the
opercula of a dental follicle.
(b) 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.
(c) The principal opercular bone in the upper and
posterior part of the gill cover.
[1913 Webster]
3. (Zool.)
(a) The lid closing the aperture of various species of
shells, as the common whelk. See Illust. of
{Gastropoda}.
(b) Any lid-shaped structure closing the aperture of a
tube or shell.
[1913 Webster]