most has 8 distinct synonyms spread across 2 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 2 recorded opposites are least, fewest.
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.
used to form the superlative
“the king cobra is the most dangerous snake”
(superlative of `many' used with count nouns and often preceded by `the') quantifier meaning the greatest in number
“who has the most apples?”
the superlative of `much' that can be used with mass nouns and is usually preceded by `the'; a quantifier meaning the greatest in amount or extent or degree
“made the most money he could”
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 most.
Synonyms, antonyms and the broader and narrower relations for most come from Princeton University’s WordNet. Full sources and licences.