The headword is present indicative middle, third person singular, of e)pistre/fw. It must be quoted from somewhere but it far too common for the source to be identifiable.
For related words see epsilon 2639, epsilon 2641, epsilon 2642, epsilon 2643. See also note 3 below.
[1] Adler cites Syntacticum Gudianum for comparison.
[2] This sentence = Synagoge epsilon743; Photius, Lexicon epsilon1731. Hesychius epsilon5262 had given the corresponding first person singular of the headword verb with two glosses, the second of them fro/ntida poiou=mai (i.e. middle rather than active). Various forms of the headword and gloss also appear together in the scholia to Sophocles, Philoctetes 598 (cited by Theodoridis on Photius s.v.), and to Homer, Iliad 18.216.
[3] Here a noun related to the headword (on which see also epsilon 2644, epsilon 2645) is glossed.