secessionist n.

1530s, from Latin secessionem (nominative secessio) "a withdrawal, separation; political withdrawal, insurrection, schism," noun of action from past-participle stem of secedere "go away, withdraw, separate; rebel, revolt," from se- "apart" (see se-) + cedere "to go" (from PIE root *ked- "to go, yield").

Originally in a Roman historical context, "temporary migration of plebeians from the city to compel patricians to address their grievances." Modern use is by 1650s in reference to "act of withdrawing from a religious or political union."

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.

1702, "to leave one's companions, go apart, retire, withdraw," from Latin secedere "go away, withdraw, separate; rebel, revolt," from se- "apart" (see se-) + cedere "to go" (from PIE root *ked- "to go, yield").

The sense of "withdraw from a political or religious alliance or union" is recorded from 1755, originally especially in reference to the ministers who left the Church of Scotland about 1733 (Seceders); later, in U.S. history, to the attempt by Southern states to separate from the union (1861). Related: Seceded; seceding.

From the Latin past-participle (secessus), English once had secess "a going away, withdrawal, retirement" (1560s), and Chauliac (early 15c.) has a noun secesse "purging of the bowels."