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1. Tired out, exhausted, as in They were whacked out after that long flight. [Slang; mid-1900s]
2. Crazy, especially under the influence of drugs. For example, She looked whacked out when the police picked her up. [Slang; mid-1900s]
mod. alcohol or drug intoxicated. Dave was so whacked out he couldn’t stand up.
3. Under the influence of a mind-altering drug.