Scheidewand
From LSJ
εἰς πέλαγος σπέρµα βαλεῖν καὶ γράµµατα γράψαι ἀµφότερος µόχθος τε κενὸς καὶ πρᾶξις ἄκαρπος → throwing seeds and writing letters at sea are both a vain and fruitless endeavor
Scheidewand, medius paries. – eine dünne Sch. zwischen etw. ziehen (bildl.), tenui muro dissaepire alqd.