mel·io·ra·tion 
(mēl′yə-rāshən, mē′lē-ə-)
(mēl′yə-rāshən, mē′lē-ə-)n.
1.
a. The act or process of improving something or the state of being improved.
b. An improvement.
2. The linguistic process by which a word over a period of time grows more elevated in meaning or more positive in connotation.