Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pĕnē̆trātor, ōris, m. [penetro], one who penetrates, a penetrator (post-class.): domus alienae penetratores, Aug. Ep. 199; Prud. Hamart. 883; Paul. Nol. Carm. 20, 285.