One who withdraws or separates himself; especially, one who withdraws from a church to which he has belonged; a seceder from an established church; a dissenter; a nonconformist; a schismatic; a sectary.

Protestant congregations that had taken the bold step of separating from the officially established Church of England.

an advocate of secession or separation from a larger group (such as an established church or a national union)

a person who thinks they should control Quebec but believes Quebec should pay her own way