seceder

noun1

1. •
   One who secedes, such as from a country or organization

   • If we now recognize this doctrine by allowing the seceders to go in peace, it is difficult to see what we can do if others choose to go or to extort terms upon which they will promise to remain. — 1861

noun2

1. •
   (historical) A follower of the 18th-century secession movement from the Church of Scotland.
2. •
   (rare) A member of the Free Presbyterian Church of Scotland.