pejoration

(pĕjˌə-rāˈshən, pēˌjə-)

1. The process or condition of worsening or degenerating.
2. Linguistics The process by which the meaning of a word becomes negative or less elevated over a period of time, as silly, which formerly meant “deserving sympathy, helpless or simple,” has come to mean “showing a lack of good sense, frivolous.”