Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
exercĭtātor, ōris, m. [exercito], an exerciser, trainer (post-Aug.), Plin. 23, 7, 63, § 121: agilitatis, id. 35, 11, 40, § 136: EQVITVM, Inscr. Orell. 3498 sq.; cf. ib. 3413.