Lewis & Short

mănūmissĭo, ōnis, f. [manumitto],

  1. I. the freeing of a slave, manumission. It was effected either per censum (when the person to be freed was registered in the census), or per testamentum, or per vindictam (v. vindicta, and Cic. Top. 2, 10); in these three cases it was called justa manumissio. A fourth mode, which, however, was less valid, consisted in pronouncing the slave free before (five) friends, or inviting him to table, or by letter, Cic. Cael. 29, 69; Gai. Inst. 1, 17; Plin. Ep. 7, 16, 4; Val. Max. 2, 6, 7; Sen. Vit. Beat. 24, 3.
  2. II. Transf., a remission of punishment, pardon, Sen. Clem. 1, 3, 1.