[1] Headword and gloss are both adjectives in the feminine dative singular. The headword is from me/las, me/laina, me/lan (LSJ s.v. at web address 1). In Homer it is used variously of emotions (fre/nes), ships, the earth, blood, water, and the sea; see Cunliffe 1963 s.v. This feminine dative singular is quoted from Homer, Iliad 1.300 (describing Achilles' ship: web address 2); cf. the scholia there, and other lexica.
[2] Homer, Iliad 1.103 (web address 3), with scholion. Cunliffe explains: "[me/lainai is] applied to the fre/nes thought of as darkened by deep emotion" (p.261).