αἱρετέος
From LSJ
ἔγνω δὲ φώρ τε φῶρα καὶ λύκος λύκον → the thief knows the thief and the wolf knows the wolf, and thief knows thief and wolf his fellow wolf, set a thief to catch a thief
English (LSJ)
α, ον,
A to be chosen, ὠφελήματα, opp. αἱρετὰ ἀγαθά, Chrysipp.Stoic.3.22, 61,al. II αἱρετέον, one must choose, Pl.Grg. 499e, Phld.Rh.1.287S., etc.