φάσθω

From LSJ

ἀμήχανον δὲ παντὸς ἀνδρὸς ἐκμαθεῖν ψυχήν τε καὶ φρόνημα καὶ γνώμην, πρὶν ἂν ἀρχαῖς τε καὶ νόμοισιν ἐντριβὴς φανῇ → hard it is to learn the mind of any mortal or the heart, 'till he be tried in chief authority | it is impossible to know fully any man's character, will, or judgment, until he has been proved by the test of rule and law-giving

Source

French (Bailly abrégé)

3ᵉ sg. impér. prés. Moy. de φημί.

Russian (Dvoretsky)

φάσθω: эп. 3 л. sing. imper. med. к φημί.