thy·ros·tra·ca \thīˈrästrəkə\noun plural Usage: capitalized Etymology: New Latin, from thyro- (from Greek thyra door, opening) + Greek ostraka, plural of ostrakon shell — more at door, oyster in some especially former classifications: a subclass of Crustacea coextensive with Cirripedia • thy·ros·tra·can\(ˈ) ̷ ̷| ̷ ̷ ̷ ̷kən\adjective or noun