Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trans-montānus, i, adj. m., that is beyond the mountains, tramontane: subactis cis Apenninum omnibus tum transmontanos adortus, Liv. 39, 2, 9; Plin. 3, 3, 4, § 28; in sing., Inscr. Orell. 154.