The headword is a feminine noun in the nominative singular; see LSJ s.v., and cf. generally omicron 1013, omicron 1014, omicron 1015, omicron 1016, omicron 1018, omicron 1019. It is a great rarity outside lexicography, and the entry has been taken to be prompted by Baruch 3:8 LXX, where it appears in the accusative singular o)/flhsin (again at Hesychius omicron1975).
[1] The first gloss is a neuter noun in the nominative/vocative/accusative singular; see LSJ s.v. The second gloss is a feminine noun in the nominative/vocative singular; see LSJ s.v. The headword is identically glossed in the Synagoge, Photius' Lexicon (omicron713), and Lexica Segueriana 323.4.