The headword is an adjective in the masculine/feminine accusative singular (and neuter nominative/vocative/accusative singular). In this form it appears to be a late (C2 CE) spelling variant of the adjective o(mwro/fios, -on (being, lodging under the same roof together with; cf. omicron 300, omicron 302, and omicron 239 (end)), attested as early as the C5 BCE (Antiphon 5.11, web address 1; see Gagarin, pp. 152-60). Considered as o(mwro/fion, the source of the present headword is taken to be Demosthenes 18.287 (web address 2); cf. the Lexicon Patmense on that passage.
[1] The gloss is an adjective of the same form as the lemma; see generally LSJ s.v. o(mo/skhnos, -on (2). The headword is identically glossed in e.g. the Synagoge, Photius' Lexicon (omicron307 Theodoridis), and Lexica Segueriana 317.31. (Also attested is a noun, o(mo/skhnos, o(, one living in the same tent, messmate; cf. LSJ s.v. o(mo/skhnos, o( (1).)