TETHYID Meaning of TETHYID in English I. ˈtethēə̇d adjectiveEtymology: New Latin Tethyidae : of or relating to the Tethyidae II. noun( -s ) : an ascidian or a mollusk of the family Tethyidae Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012