Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. rŭbĕus (rŏbeus and rŏbus; cf. Fest. s. v. robum, p. 264 Müll.), a, um, adj. [rubeo], red, reddish: color, Varr. R. R. 2, 5, 8; Col. 6, 1 fin.; 8, 2, 8; Pall. Mart. 11, 2: bos, Col. 6, 1, 2: asinus, Pall. Mart. 14, 3.
* 2. rŭbĕus, a, um, adj. [rubus], of or belonging to the bramble-bush, bramble-: virga, a bramble-twig, Verg. G. 1, 266.