ἀδιάσφαλτος
From LSJ
Ἀμήχανον δὲ παντὸς ἀνδρὸς ἐκμαθεῖν ψυχήν τε καὶ φρόνημα καὶ γνώμην πρὶν ἂν ἀρχαῖς τε καὶ νόμοισιν ἐντριβὴς φανῇ → It is impossible to know the spirit, thought, and mind of any man before he be versed in sovereignty and the laws
English (LSJ)
ον, free from error, μέθοδοι Hero *Geep.164. Adv. ἀδιασφάλτως Ps.-Dioph.p.xxi H.
Spanish (DGE)
-ον infalible μέθοδον Hero Lib.Geep.164.