The transmitted headword e)pte/rou appears to be third person singular, imperfect, of the verb ptero/w. However, in Lexica Segueriana 234.30 this same gloss attaches to e)pterou=to, and Adler notes that this was also printed in the editio princeps of the Suda. Accordingly, the headword (quoted from somewhere) and the gloss alike are more probably passive than middle.
cf. generally pi 3012.