se·ces·sion 
(sĭ-sĕshən)
(sĭ-sĕshən)n.
1. The act of seceding.
2. often Secession The withdrawal of 11 Southern states from the Union in 1860-1861, precipitating the US Civil War.
[Latin sēcessiō, sēcessiōn-, from sēcessus, past participle of sēcēdere, to secede; see SECEDE.]
se·cession·al adj.