agathism (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]

word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.