according to the Oxford English Dictionary, “The doctrine that all things tend towards ultimate good, as distinguished from optimism, which holds that all things are now for the best”. An agathist militantly accepts that evil and misfortune will ultimately happen, but that the eventual outcome leads towards the good. Or in other words, an agathist may see the world as essentially good but a place in which bad things can and do happen to good people.

Etymology: Greek agatha- (good).

[Brad Holland]