Other forms: narcs
A police detective who enforces drug laws is called a narc. Narcs often work in airports with dogs specially trained to smell various illegal drugs.
The word narc is slang shorthand for "narcotics agent," a federal agent or police officer who specializes in laws dealing with illegal drugs. Narc is sometimes also used to mean "police informant," someone who secretly gives inside information to the police, informing on others who are engaging in illegal activity. This second meaning is more often spelled "nark."