degeneration

Short definition from Wiktionary

Noun

1. 1
   The process or state of growing worse, or the state of having become worse.
2. 2
   That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure.
3. 3
   Gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type.
4. 4
   A thing that has degenerated.