Source : Webster's Revised Unabridged Dictionary (1913)

Deterioration \De*te`ri*o*ra"tion\, n. [LL. deterioratio: cf. F.
   d['e]t['e]rioration.]
   The process of growing worse, or the state of having grown
   worse.

Source : WordNet®

deterioration
     n 1: a symptom of reduced quality or strength [syn: {impairment}]
     2: process of changing to an inferior state [syn: {decline in
        quality}, {declension}, {worsening}]