narcotic
Pronunciation: /nɑːˈkɒtɪk/
noun
- an addictive drug affecting mood or behaviour, especially an illegal one: cultivation of a plant used to make a popular local narcotic
- Medicine a drug which induces drowsiness, stupor, or insensibility, and relieves pain: pethidine, usually given as an injection, is a narcotic which causes drowsiness
adjective

Origin:
late Middle English: from Old French narcotique, via medieval Latin from Greek narkōtikos, from narkoun 'make numb'