Source : Webster's Revised Unabridged Dictionary (1913)

Desuetude \Des"ue*tude\, n. [L. desuetudo, from desuescere, to
   grow out of use, disuse; de + suescere to become used or
   accustomed: cf. F. d['e]su['e]tude. See {Custom}.]
   The cessation of use; disuse; discontinuance of practice,
   custom, or fashion.

         The desuetude abrogated the law, which, before, custom
         had established.                         --Jer. Taylor.

Source : WordNet®

desuetude
     n : a state of inactivity or disuse