The headword as transmitted is a Greek genitive singular, but should surely be (by the simple addition of a final sigma) accusative plural, as in Polybius 6.26.6 on the Roman army of his time: "they first of all select for the consuls from the whole force of assembled allies the cavalrymen and infantrymen best suited for actual service -- the so-called extraordinarii, which being interpreted signifies select [men]." See pi 2242.