reform has 5 distinct synonyms spread across 2 of its 9 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
make changes for improvement in order to remove abuse and injustices
“reform a political system”
bring, lead, or force to abandon a wrong or evil course of life, conduct, and adopt a right one
“The Church reformed me”
Synonyms, antonyms and the broader and narrower relations for reform come from Princeton University’s WordNet. Full sources and licences.
produce by cracking
“reform gas”
break up the molecules of
“reform oil”
improve by alteration or correction of errors or defects and put into a better condition
“reform the health system in this country”
change for the better
“The lazy student promised to reform”
a change for the better as a result of correcting abuses
“justice was for sale before the reform of the law courts”
a campaign aimed to correct abuses or malpractices
“the reforms he proposed were too radical for the politicians”
self-improvement in behavior or morals by abandoning some vice
“the family rejoiced in the drunkard's reform”