least has 1 distinct synonym spread across 1 of its 3 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 most.
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.
something that is of no importance
“it is the least I can do”
the superlative of `little' that can be used with mass nouns and is usually preceded by `the'; a quantifier meaning smallest in amount or extent or degree
“didn't care the least bit”
Synonyms, antonyms and the broader and narrower relations for least come from Princeton University’s WordNet. Full sources and licences.
used to form the superlative
“The garter snake is the least dangerous snake”