reformist

adj

1. Advocating reform of an institution or body.

   “[...] all the prose is German, all reformist, all moralising, and has little or practically no echo of antiquity.”

2. Specifically, advocating reform and the gradual accumulation of small changes, as opposed to revolutionary action.

noun

1. One who advocates reform (of an institution).
2. Specifically, one who advocates reform of society and the gradual accumulation of small changes, as opposed to revolutionary action.
3. (dated)An advocate of reform in the Church of England; a Reformer.
4. (dated, obsolete)An advocate or supporter of political reform in the United Kingdom. (Common from ca 1790 to 1830.)
5. A member of a reformed religious denomination.