better has 9 distinct synonyms spread across 6 of its 13 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 worse, worsen.
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 superior in quality or condition or effect
“a change for the better”
a superior person having claim to precedence
“the common man has been kept in his place by his betters”
the superior one of two alternatives
“chose the better of the two”
(comparative of `good') superior to another (of the same class or set or kind) in excellence or quality or desirability or suitability; more highly skilled than another
“You're a better man than I am, Gunga Din”
(comparative of `good') changed for the better in health or fitness
“her health is better now”
(comparative and superlative of `well') wiser or more advantageous and hence advisable
“it would be better to speak to him”
to make better
“The editor improved the manuscript with his changes”
2 of the 13 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for better.
Synonyms, antonyms and the broader and narrower relations for better come from Princeton University’s WordNet. Full sources and licences.
get better
“The weather improved toward evening”