The change of something that is defective, broken, inefficient or otherwise negative, in order to correct or improve it

(transitive) To put into a new and improved form or condition; to restore to a former good state, or bring from bad to good; to change from worse to better

a political movement/party

Of Reform Judaism, its tenets, or its adherents.

An improvement (or an intended improvement) in the existing form or condition of institutions or practices, etc.; intended to make a striking change for the better in social, political or religious affairs or in the conduct of persons or operation of organizations.

One who reforms, or who works for reform. / (historical, Christianity) One who was involved in the Reformation.

present participle of reform

reformation / (chemistry) A catalytic process, whereby short-chain molecules are combined to make larger ones; used in the petrochemical industry.

simple past tense and past participle of reform

Corrected; amended; restored to purity or excellence; said, specifically, of the whole body of Protestant churches originating in the Reformation, or, in a more restricted sense, of those who separated from Martin Luther on the doctrine of consubstantiation, etc., and carried the Reformation, as they claimed, to a higher point.