agathist (n.)

1816, from Greek agathos "good" (see Agatha) + -ist.

Doctor Kearney, who formerly, with so much reputation, delivered lectures in this place on the history of Rome, observed to me once, that he was not an optimist, but an "agathist"; that he believed that every thing tended to good, but did not think himself competent to determine what was absolutely the best. The distinction is important, and seems to be fatal to the system of Optimism. [George Miller, "Lectures on the Philosophy of Modern History," Dublin, 1816]