Definition of preoperculum in English:
preoperculum
(also praeoperculum)
noun ˌpriːɒˈpəːkjʊləmˌpriːə(ʊ)ˈpəːkjʊləm
Ichthyology. The anterior of four bones forming the operculum in fishes.
Origin
Early 19th century; earliest use found in John Stark (fl. 1828). From pre- + operculum.