"discontinuance of use, practice, custom, or fashion," mid-15c., from Latin desuetudo "disuse," from desuetus, past participle of desuescere "become unaccustomed to," from de "away, from" (see de-) + suescere "become used to, accustom, habituate," from PIE *swdh-sko-, from extended form of root *s(w)e- pronoun of the third person and reflexive (referring back to the subject of a sentence); see idiom. From 1630s as "state of disuse."
