opisthureIchthyol.|ˈɒpɪsθjʊə(r)| [f. opistho- + Gr. οὐρά tail.] The posterior end of the caudal axis in the embryonic stage of some fishes, which is ultimately absorbed into the caudal fin. Hence opisˈthurala., pertaining to the opisthure. 1891Cent.Dict. cites J. A. Ryder.