désuet

obsolete, out of use, no longer in use; out of fashion, out of style, old-fashioned, passé

19th century, learned borrowing from Latin dēsuētus, past participle of dēsuēscere (“to unlearn, disaccustom”). The traditional pronunciation is that with /s/ because the Latin verb is from dē-suēscere, the first ⟨s⟩ being of the root. However, French-speakers tend to analyse it as dés-uet, which gives rise to the now predominant form with /z/.