tə̇ˈthīəˌdē noun plural
Usage: capitalized
Etymology: New Latin; in sense 1, from Tethyum, type genus + -idae; in sense 2, from Tethys, type genus + -idae
1. : a family of simple ascidians with tough leathery often brightly colored tests, large branchial sacs, and several lateral longitudinal folds — see tethyum
2. : a family of mollusks (suborder Tectibranchia) including the sea hares — see tethys