ἀδιάσφαλτος
From LSJ
ἀναγκαίως δ' ἔχει βίον θερίζειν ὥστε κάρπιμον στάχυν, καὶ τὸν μὲν εἶναι, τὸν δὲ μή → But it is our inevitable lot to harvest life like a fruitful crop, for one of us to live, one not. (Euripides, Hypsipyle fr. 60.94ff.)
English (LSJ)
ον, A free from error, μέθοδοι Hero *Geep.164. Adv. -τως Ps.-Dioph.p.xxi H.
Spanish (DGE)
-ον infalible μέθοδον Hero Lib.Geep.164.