What does "drug" mean?

Drug: Any animal, vegetable, or mineral substance used in the composition of medicines; any stuff used in dyeing or in chemical operations. Whence merchants bring Their spicy drugs. Milton.

Additional senses

  1. 2.Any commodity that lies on hand, or is not salable; an article of slow sale, or in no demand. "But sermons are mere drugs." Fielding. And virtue shall a drug become. Dryden.
  2. 3.To prescribe or administer drugs or medicines. B. Jonson.
  3. 4.To affect or season with drugs or ingredients; esp., to stupefy by a narcotic drug. Also Fig. The laboring masses . . . [were] drugged into brutish good humor by a vast system of public spectacles. C. Kingsley. Drug thy memories, lest thou learn it. Tennyson.
  4. 5.To tincture with something offensive or injurious. Drugged as oft, With hatefullest disrelish writhed their jaws. Milton.
  5. 6.To dose to excess with, or as with, drugs. With pleasure drugged, he almost longed for woe. Byron.

Sources