early 15c., "to misuse, misapply" (power, money, etc.), from Old French abuser "deceive, abuse, misuse" (14c.), from Vulgar Latin *abusare, from Latin abusus "an abusing; a using up," past participle of abuti "use up, consume," also "misuse, abuse, misapply, outrage," from ab "off, away from" (see ab-) + uti "use" (see use).
Also in reference to forbidden sexual situations from early 15c., but originally meaning incest, masturbation (self-abuse), homosexuality, prostitution, etc. From 1550s specifically as "to misuse sexually, ravish," but OED 2nd ed. marks this obsolete and the modern use "subject (someone) to unwanted sexual activity" is likely a fresh coinage from late 20c. Specifically of drugs, from 1968. Meaning "attack with harsh language, revile" is from c. 1600. Related: Abused; abusing.
mid-15c., "improper practice," from Old French abus (14c.), from Latin abusus "a using up" (see abuse (v.)). From 1570s as "violation, defilement" (surviving in self-abuse "masturbation," if at all). In reference to drugs by 1961. Modern use in reference to unwanted sexual activity is from late 20c. Earlier in Middle English was abusion "wicked act or practice, shameful thing, violation of decency" (early 14c.), "an insult" (mid-14c.), from Old French abusion, from Latin abusio.