Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
muscōsus, a, um, adj. [muscus], full of moss, mossy: prata, Varr. R. R. 1, 9, 5: fontes, Verg. E. 7, 45.
Comp.: nihil alsius, nihil muscosius, Cic. Q. Fr. 3, 1, 2, § 5.
Hence, adv.: muscōsē, mossily, Sid. Carm. 2.