This entry = ps.-Herodian 150; see also Hesychius, the Ambrosian Lexicon (according to Adler), and the scholia to Homer, Odyssey 11.189 (where the headword appears: web address 1 below).
The headword comes from a neuter variant with zero-grade suffix *xei=mn of the masculine noun xeimw/n with long o suffix (appearing here as the gloss, and see also chi 234, chi 235, chi 236).