Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
instinctor, ōris, m. [instinguo], an instigator (post-Aug.): sceleris, Tac. H. 1, 22: belli, id. ib. 4, 68; Amm. 21, 12; 30, 1.