melioration

[meel-yuh-rey-shuh n, mee-lee-uh-] /ˌmil yəˈreɪ ʃən, ˌmi li ə-/
noun
1.
Historical Linguistics. semantic change in a word to a more approved or more respectable meaning.
Compare pejoration (def 2).
2.
amelioration.
Origin
1620-30; < Late Latin meliōrātiōn- (stem of meliōrātiō), equivalent to meliōrāt(us) (see meliorate) + -iōn- -ion
British Dictionary definitions for melioration

melioration

/ˌmiːlɪəˈreɪʃən/
noun
1.
the act or an instance of improving or the state of being improved
Word Origin and History for melioration
n.

c.1400, "improvement," from Late Latin meliorationem (nominative melioratio), noun of action from past participle stem of Latin meliorare (see meliorate).