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crack (krăk)
v. cracked, crack·ing, cracks
a. To break without complete separation of parts: The mirror cracked.
b. To break or snap apart: The branch cracked off and fell.
2. To make a sharp snapping sound: His knees cracked as he sat down.
a. To break down; fail: The defendant's composure finally began to crack.
b. To have a mental or physical breakdown: cracked under the pressure.
4. To change sharply in pitch or timbre, as from hoarseness or emotion. Used of the voice.
5. To move or go rapidly: was cracking along at 70 miles an hour.
6. Chemistry To break into simpler molecules, often by means of heat or a catalyst.
a. To cause to break without complete separation of parts: The pebble cracked the car's windshield. See Synonyms at break.
b. To cause to break with a sharp snapping sound: crack nuts.
c. To crush (corn or wheat, for example) into small pieces.
a. To strike, especially with a sharp sound: cracked the intruder over the head with a lamp.
b. To cause to come into forceful contact with something, especially with a sharp sound: fell and cracked his head against the floor.
3. To open to a slight extent: crack a window to let in some air.
4. Informal
a. To break open or into: crack a safe.
b. To open up for use or consumption: crack a book; cracked a beer.
c. To break through (an obstacle) in order to win acceptance or acknowledgment: finally cracked the "men-only" rule at the club.
5. To discover the solution to, especially after considerable effort: crack a code.
6. To cause (the voice) to crack.
7. Informal To tell (a joke), especially on impulse or in an effective manner.
8. To cause to have a mental or physical breakdown.
9. To impair or destroy: Their rude remarks cracked his equanimity.
10. To reduce (petroleum) to simpler compounds by cracking.
a. A partial split or break; a fissure: cracks in the basement wall.
b. A slight narrow space: The window was open a crack.
c. Informal The fissure between the buttocks.
2. A defect or flaw: cracks in the argument; a crack in his composure.
3. A sharp snapping sound, such as the report of a firearm.
4. A sharp resounding blow: gave him a crack on the head.
5. A breaking, harshly dissonant vocal tone or sound, as in hoarseness.
6. An attempt or try: gave him a crack at the job; took a crack at photography.
7. A witty or sarcastic remark. See Synonyms at joke.
8. A moment; an instant: at the crack of dawn.
9. Irish Fun had when socializing; social amusement.
10. Slang Crack cocaine.
Excelling in skill or achievement; first-rate: a crack shot; a crack tennis player.
Phrasal Verbs:
crack down
To act more forcefully to regulate, repress, or restrain: The police cracked down on speeding.
crack up Informal
1. To praise highly: He was simply not the genius he was cracked up to be.
a. To damage or wreck (a vehicle or vessel): crack up a plane; crack up a boat.
b. To wreck a vehicle in an accident: cracked up on the expressway.
3. To have a mental or physical breakdown: crack up from overwork.
4. To experience or cause to experience a great deal of amusement: really cracked up when I heard that joke.
crack the whip
To behave in a domineering manner; demand hard work and efficiency from those under one's control.

[Middle English craken, from Old English cracian; see gerə-2 in the Appendix of Indo-European roots.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.