Secede is to separate or formally withdraw from a group or community.(verb)
When the South wanted to leave the Union prior to the Civil War, this is an example of a situation where the South tried to secede.
See secede in Webster's New World College Dictionary
See secede in American Heritage Dictionary 4
intransitive verb se·ced·ed, se·ced·ing, se·cedes
Origin: Latin sēcēdere, to withdraw
Origin: : sē-, apart; see s(w)e- in Indo-European roots
Origin: + cēdere, to go; see ked- in Indo-European roots.
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