Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ossa, ae, f. (m., Ov. M. 1, 155), = Ὄσσα, a high mountain in Thessaly, now Kissovo, Mel. 2, 3, 2; Plin. 4, 8, 15, § 30: ter sunt conati imponere Pelio Ossam, Verg. G. 1, 281: Ossan, Ov. F. 1, 307.
Hence, Ossaeus, a, um, adj., Ossean: saxa, Verg. Cir. 33: rupes, Luc. 6, 334: media, Stat. Th. 2, 82: Ossaei bimembres, i. e. the Centaurs who dwell about Ossa, id. ib. 12, 554.