Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dū̆pondĭus, ii, m., or dŭpondĭum, ii (cf. Varr. L. L. 9, 49, § 81; also, dĭpon-dĭum, Gromat. Vet. p. 28, 14; p. 167, 11), n. [duo-pondus], the sum of two asses.