The mss. vary between ἐξιτήριον and ἀλεξιτήριον, farewell gift and amulet or charm.  In Ep. cciii. 299 Basil says that our Lord gave His disciples peace as an ἐξιτήριον δῶρον, using the word, but in conjunction with δῶρον.  Greg. Naz., Orat. xiv. 223 speaks of our Lord leaving peace “ὥσπερ ἄλλο τι ἐξιτήριον.”