Same entry in ps.-Zonaras and, according to Adler, the Ambrosian Lexicon 39.
The headword is an epic contracted form of kata/moros ('adversely-fated'), although ancient scholars tend to analyze it as deriving from kako/moros ('bad-fated') by syncope: Etymologicum Gudianum 297.6, Etymologicum Magnum 488.42; cf. Apollonius' Homeric Lexicon 95.7, and Hesychius kappa604. Found requently in the masculine vocative singular in Homer's Odyssey: e.g. 5.160 (web address 1), 11.216, etc.
If the present entry's nominative singular has been quoted from somewhere in that form, a possible source is Greek Anthology 7.621.2; alternatively this is simply a paradigmatic nominative generated by a vocative (cf. next note).
[1] The same gloss is used (in the vocative) in the scholia to Homer, Odyssey 5.160.