The headword is a masculine noun in the nominative singular; see LSJ s.v., and cf. omicron 175 and omicron 180. (There is also an adjective, o(lko/s, -h/, -o/n, drawing to oneself, attractive; cf. omicron 177, omicron 178, and omicron 179.)
[1] The glossing substantives are all in the nominative singular: the first and last are feminine nouns, and the second is a two-ending feminine (and masculine) adjective; see LSJ s.vv., and cf. Hesychius omicron588 s.v. o(lko/s, and Etymologicum Magnum 622.8.
[2] The sense of o(lko/s as a trail is noted by both John Philoponus, De vocabulis quae diversum significatum exhibent secundum differentiam accentus s.v. o(/lkos, and the scholia (247.9 Rabe) to Lucian, Hermotimus 79, where the genitive occurs.
[3] Same entry in the Synagoge, Photius' Lexicon (omicron231 Theodoridis), and Lexica Segueriana 316.21-24. On what is being described see generally LSJ s.v., I: machine for hauling ships, hauling-engine (with references).