Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dūmus (old form dusmus, v. dumosus), i, m. [dusmus for densimus, from densus], a thorn-bush, bramble, Cic. Tusc. 5, 23, 65; Verg. G. 3, 315; 338; 4, 130; id. A. 4, 526 et saep.