Is it ensure, insure, or assure?
1794 (n.) in the theological sense "one who affirms the humanity of Christ but denies his pre-existence and divinity," from humanity + suffix from unitarian, etc.; see humanism. Meaning "philanthropist, one who advocates or practices human action to solve social problems" is from 1842, originally disparaging, with a suggestion of excess. As an adjective, by 1834.