неисповедимый

From LSJ

ὕδωρ δὲ πίνων οὐδὲν ἂν τέκοι σοφόν → by drinking water you would never create anything great

Source

Russian > Greek

ἄβυσσος, ἀνεξιχνίαστος, ἀτέκμαρτος, ἀπέρατος