Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
simpŭvĭum, ii, n., a vessel for offering liquids, esp. wine, in sacrifices, a sacrificial bowl (cf.: patera, poculum), Varr. ap. Non. 544, 30; Cic. Rep. 6, 2, 11; Plin. 35, 12, 46, § 158 (Jahn, simpuis); Juv. 6, 343; Arn. 7, 235; cf. Becker, Gallus, 2, p. 280 (2d edit.).