Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dĕcŭrĭōnātus, ūs, m. [2. decurio], the office and dignity of a decurion; of cavalry, Cato ap. Fest. p. 201, 28 M.; in the municipia, Traj. ap. Plin. Ep. 10, 114; Dig. 50, 2, 2 sq.; Inscr. Orell. 164 al.