The Collaborative International Dictionary of English v.0.48:
Ideologist \I`de*ol"o*gist\, n. 1. One who treats of ideas; one who theorizes or idealizes; one versed in the science of ideas, or who advocates the doctrines of ideology. 2. An ideologue. [PJC]WordNet (r) 3.0 (2006):
ideologist n 1: an advocate of some ideology [syn: ideologist, ideologue]