obsolescent

adjective

1. becoming obsolete; passing out of use, as a word: an obsolescent term.
2. becoming outdated or outmoded, as machinery or weapons.
3. Biology. gradually disappearing or imperfectly developed, as vestigial organs.

adjective

1. becoming obsolete or out of date

adj.1755, from Latin obsolescentum (nominative obsolescens), present participle of obsolescere “fall into disuse” (see obsolete).