The headword is an adverb, which also functions as a preposition with the dative or, more usually, genitive case. It derives from the verb e)/xw (aorist e)/sxon). LSJ s.v. gives lavish documentation of its primary senses and applications (to place and time), together with its post-Homeric manifestation(s) as a multi-purpose term meaning about approximately, more or less, roughly speaking. See web address 1.
The glossing here is also in Photius (sigma898 Theodoridis) and other lexica, and cf. the scholia to Homer, Iliad 3.15.