Meth/meθ/ Definition 1 of 2Pro Tip 1/3Illegal Substance Meth refers to a prohibited drug with serious legal consequences if possessed or sold. Many campaigns aim to prevent meth abuse. Pro Tip 2/3Addictive Drug Meth is highly addictive, often associated with severe health and social issues. She's in rehab for meth addiction. Pro Tip 3/3Slanguage 'Meth' is slang and used in informal, often illegal, contexts. The police found a meth lab in the basement.