φαῖσι
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
Greek (Liddell-Scott)
φαῖσι: φασί, Σαπφ. Ἀποσπ. 56, ἔκδ. Bergk ἐκ Lyr. gr. ― Ἴδε καὶ τὰ παρὰ τῷ Kühner Aysführl. Gram. d. gr. Spr. I, σ. 116 παρατεθειμένα· δίψαισι (ἐκ τοῦ δίψημι), πεπάγαισιν, κεκρίκαισιν, τὰ ἐκ τοῦ Ἀλκαίου.