The headword is the present active infinitive of the contract verb fwra/w, I search after a thief; cf. phi 663, phi 666, and see generally LSJ s.v. It is apparently generated by Plato, Laws 954A-B (where the first of the glossing infinitives also occurs: web address 1): the Athenian lays out guidelines for searching another person's house for missing property.
[1] The glosses are the same form as the headword. The first is from the contract verb e)reuna/w (I enquire after); the second from the contract verb e)kzhte/w (I seek out); see generally LSJ s.vv. The lexicographer is following a scholion (= scholia vetera) to the aforementioned Platonic text. The headword is identically glossed in Etymologicum Magnum 804.9 (Kallierges) and, earlier, in Timaeus' Platonic Lexicon phi1007a14 (which, however, transmits the spelling variants fwra=|n and e)reuna=|n). (Adler also cites Etymologicum Genuinum as identical.) For other references see Photius phi373 Theodoridis, and cf. generally the scholia (4.10 Rabe) to Lucian, Phalaris 1.4.