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
ūrēthra: ae, f., = οὐρήθρα,
I the excretory canal of the urine, the urethra, Cael. Aur. Tard. 5, 4, 66; 5, 10, 91.