WordNet records no synonym and no antonym for probabilism. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a Roman Catholic system of casuistry that when expert opinions differ an actor can follow any solidly probable opinion that he wishes even though some different opinion might be more probable
(philosophy) the doctrine that (since certainty is unattainable) probability is a sufficient basis for belief and action
Synonyms, antonyms and the broader and narrower relations for probabilism come from Princeton University’s WordNet. Full sources and licences.