Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
arquātus, a, um, adj. [arquus = arcus = rainbow; v. arcus init.]: morbus, the jaundice (a disease in which the skin turns to the yellow color of the rainbow), Cels. 3, 24.
Hence, subst.: arquātus, i, m., one that has the jaundice, Non. p. 425, 3: Lurida praeterea flunt, quaecumque tuentur Arquati, Lucr. 4, 332 sq.; Varr. ap. Non. p. 35, 16; Col. 7, 5, 18; and Plin. 20, 11, 44, § 115.