ἄστριος

From LSJ

Δελφῖνα νήχεσθαι διδάσκεις: ἐπὶ τῶν ἐν ἐκείνοις τινὰ παιδοτριβούντων, ἐν οἷς ἤσκηται → Teaching dolphins to swim: is applied to those who are teaching something among people who are already well versed in it

Source

Spanish (DGE)

-ου, ὁ n. de una piedra preciosa Dsc.5.142; cf. ἀστέριος 3.