οὐραῖον

From LSJ

μέτρον γὰρ τοῦ βίου τὸ καλόν, οὐ τὸ τοῦ χρόνου μῆκος → for life's measure is its beauty not its length (Plutarch, Consolatio ad Apollonium 111.D.4)

Source

Russian (Dvoretsky)

οὐραῖον: τό
1 хвост (κυνός Men.);
2 хвостовой плавник или рыбий хвост Arst.