manumission

In the United States before the Civil War, when owning slaves was common, manumission was the act of setting a slave free.

When Hamilton sings about "revolutionary manumission abolitionists" in the musical Hamilton, he's being a tiny bit redundant. Manumission and abolition are both used to mean "freeing slaves" or "a release from slavery." More specifically though, manumission is the act of a slave owner setting slaves free, while emancipation (and abolition) involve government action. When slavery was legal in the U.S., most who opposed it believed in all three.

Definitions of manumission
1

n the formal act of freeing from slavery

“he believed in the manumission of the slaves”
Type of:
freeing, liberation, release
the act of liberating someone or something

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