Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
compŏsĭtor (conp-), ōris, m. [compono], an orderer, arranger, disposer, maker (rare): inventor aut compositor aut actor, Cic. Or. 19, 61: anni, id. Leg. 2, 12, 29 (al. compositio): operum, Ov. Tr. 2, 356: juris, Cod. Just. 6, 28, 4: historiae Cumanae, Fest. p. 266, 26 Müll.: melodiae, Cassiod. Hist. Eccl. 1, 2 fin.