pej·o·ra·tion 
(p
ĕj
′ə-r
āsh
ən, p
ē′j
ə-)
n.1. The process or condition of worsening or degenerating.
2. Linguistics The process by which the meaning of a word becomes negative or disparaging over a period of time, as silly, from Middle English seely, "blessed, innocent," has come to mean "showing a lack of good sense, frivolous."
[Medieval Latin pēiōrātiō, pēiōrātiōn-, from Late Latin pēiōrātus, past participle of pēiōrāre, to make worse, from Latin pēior, worse; see ped- in the Appendix of Indo-European roots.]