Of words: Disused, obsolete. Obsolete.

spec. Of a language: still in vernacular use. Cf. dead language n. at dead, adj. n.adv. compounds 2.

Dead.

Designating the form of a language that is currently used, or the form representing the most recent significant stage of development, as opposed to…

Philology. Modifying the name of a language: denoting a period in the history of a language (and the variety or varieties of the language used during…

esp. of language: Belonging to an earlier period, no longer in common use, though still retained either by individuals, or generally, for special…

Linguistics. Of or relating to a relict (relict, n. 3f); (of a word, form, language, etc.) that is a relict.