The headword is a masculine noun in the accusative singular; see LSJ s.v. o(/rmos, -ou, o(. It is taken to be extracted from Homer, Iliad 1.435 (web address 1); cf. the scholia there, glossing ei)s o(/rmon (into an anchorage) with ei)s to\n lime/na (into the harbor). On this sense of the headword see generally LSJ s.v., II.
[1] The gloss is the masculine accusative singular form of the noun limh/n, harbor, haven, creek; see LSJ s.v. The headword is identically glossed in Photius' Lexicon (omicron496 Theodoridis) and at Lexica Segueriana 320.26; cf. Hesychius omicron1260, and Etymologicum Magnum 631.30 (Kallierges). John Philoponus, De vocabulis quae diversum significatum exhibent secundum differentiam accentus s.v. o(/rmos interprets the present paroxytone (accent on the penult; Smyth, 157) form of the headword as meaning limh/n (harbor) and gives an oxytone (accent on the ultima, ibid.) form, o(rmo/s (necklace); cf. omicron 604. Adler also cites the Lexicon de Spiritu, L.C. Valckenaer, ed.
[2] Aelian fr. 79 Hercher (fr. 82 Domingo-Forasté, p. 67), which includes not the headword itself but a noun similar in meaning: o(/rmisis. In her critical apparatus, Adler notes that mss. GFS and, before correction, mss AM transmit o(/rmhsin, the accusative singular form of the feminine noun o(/rmhsis, -ews, h( (thus, in their rapid motion); see LSJ s.v. Literally, o(/rmisis, -ews, h(, which occurs here in the accusative singular, means bringing a ship to anchor; see LSJ s.v. In the present sense, though, it is evidently metaphorical and means dying, as LSJ observes s.v. o(rmi/zw, II.2 (I bring to safe anchorage; cf. omicron 603), with reference in particular to the quoted Aelian fragment.