narcotic

Short definition from Wiktionary

Noun

1. 1
   Any substance or drug that reduces pain, induces sleep and may alter mood or behaviour; in some contexts, especially in reference to the opiates-and-opioids class, especially in reference to illegal drugs, and often both.
2. 2
   Any type of numbing or soothing drug.

Adjective

1. 1
   Of, or relating to narcotics.
2. 2
   Inducing sleep; causing narcosis.