The headword is a feminine noun in the nominative (and vocative) singular; see generally LSJ s.v., and cf. the related adjective at pi 2254. It might be quoted from somewhere in this form (see next note), or else generated by e.g. Herodotus 6.51.1 (web address 1), where the Ionic accusative singular form presbugenei/hn appears in material on the two royal families of Sparta.
[1] Same or similar glossing in other lexica; references at Photius pi1153, where Theodoridis suggests that the headword is quoted from Basil of Caesarea (PG 29.13c).
[2] This addendum is longer in some of the lexica, kai\ sugkritikw=s prou)rgiai/teron (cf. pi 2909), and as such is discernible as displaced from a lemma prou)/rgou (pi 2912).