briefness
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)
subs.
P. βραχύτης, ἡ.
Of speech: P. βραχυλογία, ἡ.
Conciseness: P. συντομία, ἡ.