probability has 1 distinct synonym spread across 1 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is improbability.
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 measure of how likely it is that some event will occur; a number expressing the ratio of favorable cases to the whole number of cases possible
“the probability that an unbiased coin will fall with the head up is 0.5”
Synonyms, antonyms and the broader and narrower relations for probability come from Princeton University’s WordNet. Full sources and licences.
the quality of being probable; a probable event or the most probable event
“for a while mutiny seemed a probability”