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zonk out

When you zonk out, you fall asleep suddenly. You may have seen babies be wide awake one minute and then zonk out the next.

A college student who was awake all night writing a paper might zonk out, and a toddler who refused to take an afternoon nap will usually zonk out at bedtime. You can also use the informal phrase to describe what happens when someone faints or is knocked unconscious. The word zonk became a popular slang term for "hit hard" in the 1950s, probably because the word sounds like the action of banging someone over the head.

Definitions of zonk out
  1. verb
    fall asleep fast, as when one is extremely tired
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    type of:
    dope off, doze off, drift off, drop off, drowse off, fall asleep, flake out, nod off
    change from a waking to a sleeping state
  2. verb
    lose consciousness due to a sudden trauma, for example
    synonyms: black out, pass out
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    types:
    conk, faint, pass out, swoon
    pass out from weakness, physical or emotional distress due to a loss of blood supply to the brain
    type of:
    change state, turn
    undergo a transformation or a change of position or action
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