Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rŏsētum, i, n. [rosa], a garden or bed of roses, a rosary, Varr. R. R. 1, 35; Verg. E. 5, 17; Claud. Nupt. Hon. 8; Pall. 12, 11.