Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dēmonstrātor, ōris, m. [demonstro], one who points out or indicates; an indicator, exhibiter (very rare): uniuscujusque sepeliendi, * Cic. de Or. 2, 86, 353: hujus rationis, Col. 3, 10, 20: medicinarum Aesculapius, Tert. Apol. 23.