Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rŭbĭa, ae, f. [1. rubeus], madder, Plin. 19, 3, 17, § 47: quam aliqui ereuthodanum vocant, id. 24, 11, 56, § 94; 35, 6, 26, § 45; Vitr. 7, 14.