operculum noun. [ǝ(ʊ)'pǝ:kjʊlǝm] Pl. -la [-lǝ]. E18.
[Latin = lid, covering, from operire to cover: see -CULE.]
1. Zoology. Any of various structures covering or closing an aperture; esp. (a) the bony flap covering the gills of a fish; (b) the calcareous, horny, or fibrous plate secreted by some gastropod molluscs, serving to close the aperture of the shell when the animal is retracted. E18.

2. Botany.
a. The lid of the capsule in mosses, covering the peristome. L18.
b. The cap of the ascus in certain ascomycetous fungi. L19.

3. gen. A cover. M19.
Time The..'grandfather clock' pediment with its round operculum.

[TahlilGaran] English Dictionary ▲