desuetude
The state when something (for example, a custom or a law) is no longer observed nor practised; disuse, obsolescence.
uncountable
And they being in a capacity to forget by reaſon of deſuetude, it will be a nevv pleaſure to them to recall to minde their almoſt obliterate ſpeculations.
The state when something (for example, a custom or a law) is no longer observed nor practised; disuse, obsolescence. — An instance of this.
countable
Owing, I will believe, to Fred's sudden flurry in the unprovided moment,—unprovided, by reason of prior desuetudes and discouragements to speech, on Papa's side.
Chiefly followed by from or of: a cessation of practising or using something.
countable, obsolete
[T]he beſt Chriſtians, and (vvitneſs David) the greateſt Proficients in Scripture-Knovvledge, have the keeneſt Stomacks to this Food of Souls; and the vigorouſeſt Piety, by a Deſuetude and Neglect of it, is ſubject to Faint and Pine avvay.
Where it comes from
From Late Middle English desuetude, dissuetude (“discontinuance of a practice, disuse”), from Middle French désuétude (“obsolescence”) (modern French désuétude), from Latin dēsuētūdo (“discontinuance of a practice or a habit, disuse”), from dēsuētus + -tūdō (“suffix forming abstract nouns indicating conditions or states”). Dēsuētus is the perfect passive participle of dēsuēscō (“to make unaccustomed”), from de- (prefix having a reversing or undoing effect) + suēscō (“to become accustomed or used to; (Late Latin) to accustom, habituate, train”) (ultimately from Proto-Indo-European *swé (“self”) + *dʰeh₁- (“to do; to place, put”), in the sense “to set as one’s own”).
Adapted from the Wiktionary entry desuetude (CC BY-SA 4.0).