The headword is unattested elsewhere, but is probably a variant for the nominative/accusative plural of xi/metlon/xei/metlon ('chilblain'); cf. chi 313 and the similar entry at Etymologicum Magnum 811.55. The gloss of this entry thus alludes to the fact that xe/metla derives from xeimw/n ('winter') with a loss of diphthongization in the same way that xe/rniba (chi 209, chi 210) loses the diphthong of its root, xei/r ('hand'); cf. ps.-Herodian 3.2.605.
The entry perhaps derives ultimately from commentary on Aristophanes, Wasps 1167, where the singular form of the headword (with -i- rather than -e-) occurs (web address 1).