1520s, "disaccustomed, not wonted" (a sense now obsolete), past-participle adjective from disuse (v.). Meaning "no longer used, abandoned" is from 1610s.
Entries linking to disused
disuse v.
c. 1400, disusen, "to misuse, pervert;" mid-15c., "become unaccustomed" (both senses now obsolete), from or on analogy of Old French desuser, from des- "not" (see dis-) + user "use" (see use (v.)). Meaning "cease to use, neglect to employ" is from late 15c.