Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Trĭōnes, um, m. (orig. the ploughingoxen; cf. Varr. L. L. 7, § 74 sq. Müll.; Gell. 2, 21, 7; hence, transf.), the constellation of the Wain, i. e. Ursa Major and Ursa Minor (which were compared to a wagon with oxen yoked to it): Arcturum pluviasque Hyadas geminosque Triones, Verg. A. 3, 516: gelidi, Ov. M. 2, 171: Hyperborei, Mart. 9, 46, 1: Odrysii, id. 7, 80, 1: pigri, Claud. III. Cons. Hon. 205: inoccidui, id. Gigantom. 11; Ov. M. 10, 446.