Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
transversārĭus, a, um, adj. [transversus], lying across, cross-. transverse: tigna, cross-beams, Caes. B. C. 2, 15.
As subst.: transversārĭa, ōrum, n. (sc. ligna), cross-beams, Vitr. 8, 6; 10, 11 fin.