Δίαρχοι
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 (LSJ)
οἱ, the Hellenodicae, Hsch.
Greek (Liddell-Scott)
Δίαρχοι: οἱ, οἱ δύο Ἑλλανοδίκαι, Ἡσύχ.