The headword is a two-ending adjective, here in the neuter nominative/vocative/accusative singular (and masculine/feminine vocative singular); see LSJ s.v. nhpenqh/s, -e/s. It is quoted here from the beginning of a line of Homer: see below.
[1] The gloss is the same form as the headword, from the two-ending adjective a)penqh/s, -e/s; see LSJ s.v. Same gloss in Apollonius's Homeric Lexicon (116.29); Photius, Lexicon nu192 Theodoridis; and Lexica Segueriana 308.27; cf. Hesychius nu497 and the scholia to Homer, Odyssey 4.221 (web address 1). [In her critical apparatus, Adler notes that the glossing word was omitted by mss GM.]
[2] Homer, Odyssey 4.221 (web address 1), used of a drug; cf. Hesychius s.v. a)/xolon (end). [After the quoted passage, mss GFVM append a)nti\ tou= a)penqe/s, meaning without grief (so Adler).]