SECESSIONIST
secessionist
(noun) an advocate of secessionism
Source: WordNet® 3.1
Etymology
Noun
secessionist (plural secessionists)
A person who secedes or supports secession from a political union or an alliance or organisation.
Usage notes
A common usage is for supporters of the Confederacy during the United States Civil War.
Adjective
secessionist (comparative more secessionist, superlative most secessionist)
seceding or supporting secession.
Usage notes
As well as being applied to people and movements, 'secessionist' is commonly used to describe opinions or beliefs and the form of their expression in books, articles, or speeches.
Source: Wiktionary
Se*ces"sion*ist, n.
1. One who upholds secession.
2. (U.S. Hist.)
Definition: One who holds to the belief that a State has the right to
separate from the Union at its will.
Source: Webster’s Unabridged Dictionary 1913 Edition