late 14c., reformen, "to convert into or restore to another and better form" (of strength, health, firmness, etc.), from Old French reformer "rebuild, reconstruct, recreate" (12c.) and directly from Latin reformare "to form again, change, transform, alter," from re- "again" (see re-) + formare "to form" (see form (n.)).
The meaning "change (someone or something) for the better, correct, improve; bring (someone) away from an evil course of life" is recorded from late 14c.; of governments, institutions, etc., from early 15c. Intransitive sense of "abandon wrongdoing or error" is by 1580s. Related: Reformed; reforming. Reformed churches (1580s) on the European continent were usually Calvinist as opposed to Lutheran (in France they were the Huguenots). Reformed Judaism (1843) is a movement initiated in Germany by Moses Mendelssohn (1729-1786). Reform school is attested from 1859.
mid-15c., "corrector, improver; mediator, negotiator," agent noun from reform (v.). From 1540s as "one who leads or assists the religious movements of the 16c. aimed at reformation of Christianity;" also "one who promotes or favors reform in certain practices of things."
1580s, originally religious, "a Protestant;" from reform + -ist. Political sense of "one who proposes or favors reform to the order of society," with varying specifics, is from 1640s. Related: Reformism (1904), which was specifically the theory that socialism might be established gradually via a nation's own institutions rather than only by revolution.
"form again, remake, reconstruct, re-create or re-establish," mid-14c., from re- "back, again" + form (v.). Intransitive sense of "form again, get into order or line again" also is from mid-14c. Spelled with a hyphen from 17c. to distinguish it from the specific sense in reform; this is the original meaning of that word, still in use but now with full pronunciation of the prefix. Related: Re-formed; re-forming; re-formation.
mid-14c., redressen, "to correct, reform" (a person; a sense now obsolete); late 14c., "restore, put right" (a wrong, error, offense); "repair; relieve; improve; amend," from Old French redrecier, redresier, "reform, restore, rebuild" (Modern French redresser), from re- "again" (see re-) + drecier "to straighten, arrange" (see dress (v.)). Formerly used in many more senses than currently. Related: Redressed; redressing.