A term referring to someone addicted to psychoactive
drugs, opiates in particular, and especially those using heroin (an opiate). The term was coined during WW1 when heroin or morphine addicts collected and sold scrap metal (junk) for a higher price to buy their
drugs. After this, heroin and morphine themselves began to be known as "junk" and the users of said
drugs became known as "junkies".