Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
bĭtūmĭnōsus, a, um, adj. [bitumen], abounding in bitumen, bituminous (perh. only in the two foll. exs.): terra, Vitr. 8, 3, 9: fontes, id. 8, 3, 4.