Source : Webster's Revised Unabridged Dictionary (1913)

Manumission \Man`u*mis"sion\, n. [L. manumissio: cf. F.
   manumission. See {Manumit}.]
   The act of manumitting, or of liberating a slave from
   bondage. ``Given to slaves at their manumission.''
   --Arbuthnot.

Source : WordNet®

manumission
     n : the formal act of freeing from slavery; "he believed in the
         manumission of the slaves"