Disuse through long neglect. A law, custom, word, or ritual falls into desuetude when it is left behind until it no longer governs and is barely remembered. The abandonment is quiet, a fading out rather than a replacement.

From Latin dēsūētūdō “unaccustomedness,” from de- “away from” + suēscere “to become accustomed” (related to suētus “accustomed”). What falls into desuetude is not defeated; it is simply no longer practiced, and practice is how rules stay alive.