likely has 6 distinct synonyms spread across 3 of its 5 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 unlikely.
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.
has a good chance of being the case or of coming about
“these services are likely to be available to us all before long”
with considerable certainty; without much doubt
“He is probably out of the country”
1 of the 5 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for likely.
Synonyms, antonyms and the broader and narrower relations for likely come from Princeton University’s WordNet. Full sources and licences.