Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ĕquīso, ōnis, m. [equus], a groom, stableboy (ante- and post-class.), Varr. ap. Non. 105, 14; 32 sq.; Val. Max. 7, 3 ext. 2; App. M. 7, p. 194: equisones nautici, who draw vessels along by ropes, Varr. ap. Non. 106, 1; id. 451, 4.