sisterhood
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
English > Greek (Woodhouse)
substantive
o Ismene joined to me in sisterhood: V. ὦ κοινὸν αὐτάδελφον Ἰσμήνης κάρα (Soph., ant. 1).