A lid-like structure covering certain cestode and most trematode eggs.
n. (pl. opercula) 1. a plug of mucus that blocks the cervical canal of the uterus in a pregnant woman. When the cervix begins to dilate at the start of labour, the operculum, slightly stained with blood, comes away as a discharge (‘show’). 2. (in embryology) a plug of fibrin and blood cells that develops over the site at which a developing fertilized ovum has become embedded in the wall of the uterus. 3. (in neurology) one of the folded and overlapping regions of cerebral cortex that conceal the *insula on each side of the brain. 4. (in dentistry) a flap of gingival tissue that overlies the crown of a partially erupted tooth.
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