καθέω

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

Russian (Dvoretsky)

καθέω: (только 3 л. sing. aor. καθεῖσε, 3 л. pl. aor. κάθεσσαν, 3 л. pl. conjct. καθέσωσι; med.: 3 л. sing. aor. καθέσσατο и 3 л. pl. aor. κᾰθέσσαντο) Hom., Pind., Anacr., Thuc. = καθίζω.