Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ŏpĕrātor, ōris, m. [operor], a worker, operator (post-class.), Firm. Math. 3, 9; Tert. Exhort. ad Castit. 3; id. Apol. 23 fin. al.; Lact. 6, 18, 13; Vulg. Prov. 22, 2.