Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
exercĭtĭum, ii, n. [exerceo], exercise (postAug.; not in Cic. and Caes.): frequentibus exercitiis praeparare milites ad proelia, Sall. Fragm. ap. Veg. Mil. 1, 9 fin.: equitum, Tac. A. 2, 55; cf. Vell. 2, 109: aliarum quoque rerum vel studio vel exercitio eum teneri, Gell. 3, 1, 12: in exercitiis disci, i. e. plays, Vulg. 2 Macc. 4, 14.