Webster's 1913 Dictionary
OPERCULUM
O *per "cu *lum, n.; pl. L. Opercula, E. Operculums. Etym: [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.
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.
3. (Zoöl.) (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.
New American Oxford Dictionary
operculum
o per cu lum |ōˈpərkyələm oʊˈpərkjələm | ▶noun ( pl. opercula |-lə | ) Zoology & Botany a structure that closes or covers an aperture, in particular: • technical term for gill cover. • a secreted plate that serves to close the aperture of a gastropod mollusk's shell when the animal is retracted. • a lidlike structure of the spore-containing capsule of a moss. DERIVATIVES o per cu lar |-lər |adjective, o per cu late |-ˌlāt |adjective, o per cu li- comb. form ORIGIN early 18th cent.: from Latin, literally ‘lid, covering, ’ from operire ‘to cover. ’
Oxford Dictionary
operculum
operculum |ə (ʊ )ˈpəːkjʊləm | ▶noun ( pl. opercula |-lə | ) Zoology & Botany a structure that closes or covers an aperture, in particular: • technical term for gill cover. • a secreted plate that closes the aperture of a gastropod mollusc's shell when the animal is retracted. • a lid-like structure of the spore-containing capsule of a moss. DERIVATIVES opercular adjective, operculate |-lət |adjective, operculi- combining form ORIGIN early 18th cent.: from Latin, literally ‘lid, covering ’, from operire ‘to cover ’.
The Wordsmith Dictionary