Merriam-Webster Collegiate Dictionary - opiate

 I. noun  Date: 15th century  1.  a. a drug (as morphine or codeine) containing or derived from opium and tending to induce sleep and alleviate pain; broadly narocotic 1a  b. opioid 1  2. something that induces rest or inaction or quiets uneasiness  II. adjective  Date: 1543  1.  a. containing or mixed with opium  b. of, relating to, binding, or being an ~ ~ receptors  2.  a. inducing sleep ; narcotic  b. causing dullness or inaction