δυσαπόδεικτος
From LSJ
εἰ ἀποκρυπτόντων τῶν Μήδων τὸν ἥλιον ὑπὸ σκιῇ ἔσοιτο πρὸς αὐτοὺς ἡ μάχη καὶ οὐκ ἐν ἡλίῳ → if the Medes hid the sun, the battle would be to them in the shade and not in the sun
English (LSJ)
ον,
A hard to demonstrate, Pl.R.488a.
German (Pape)
[Seite 676] schwer zu beweisen, Plat. Rep. VI, 487 e.