desuetude \DES-wih-tood, -tyood\ (noun) - The cessation of use; discontinuance of practice or custom; disuse.
"Though access for such purposes had formerly been denied, the custom had fallen into desuetude; and in contemplating her possible difficulties, she was again almost driven to fall back upon her husband." -- Thomas Hardy, 'The Withered Arm'
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Desuetude comes from Latin desuetudo, "disuse," from desuescere, "to become unaccustomed," from de- + suescere, "to become used or accustomed."