/meel'yeuh ray"sheuhn, mee'lee euh-/ , n.
1. Historical Ling. semantic change in a word to a more approved or more respectable meaning. Cf. pejoration (def. 2).
2. amelioration.
[ 1620-30; melioration- (s. of melioratio ), equiv. to meliorat ( us ) (see MELIORATE) + -ion- -ION ]