Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dossŭārĭus, a, um, adj. [dorsum], that carries on its back, that bears burdens (very rare): aselli, Varr. R. R. 2, 6 fin.: jumenta, beasts of burden, id. ib. 2, 10, 5.