What does agathist mean?

agathist meaning in Etymology Dictionary

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, noticed in my experience as soon as, that he was not an optimist, but an "agathist"; which he believed that every thing tended to good, but failed to believe himself competent to determine that which was definitely the best. The difference is essential, and is apparently fatal on system of Optimism. [George Miller, "Lectures regarding the Philosophy of contemporary History," Dublin, 1816]