Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
nĕgātor, ōris, m. [nego], a denier (postclass.), Tert. adv. Haer. 11; Prud. Cath. 1, 57: Jovis et Minervae, Sid. Ep. 9, 16.