Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trāgum, i, n., a kind of pap or porridge, Phn. 18, 7, 16, § 76; Cels. 2, 20.
Called also trāgŏs, Plin. 18, 10, 20, § 93.