<p><strong>Verb (used without object)</strong></p><ul><li>to break without complete separation of parts; become fissured: The plate cracked when I dropped it, but it was still usable.</li><li>to break with a sudden, sharp sound: The branch cracked under the weight of the snow.</li><li>to make a sudden, sharp sound in or as if in breaking; snap: The whip cracked.</li><li>(of the voice) to break abruptly and discordantly, especially into an upper register, as because of weariness or emotion.</li><li>to fail; give way: His confidence cracked under the strain.</li><li>to succumb or break down, especially under severe psychological pressure, torture, or the like: They questioned him steadily for 24 hours before he finally cracked.</li><li>Chemistry: to decompose as a result of being subjected to heat.</li><li>Chiefly South Midland and Southern U.S.: to brag; boast.</li><li>Chiefly Scot: to chat; gossip.</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>to cause to make a sudden sharp sound: The driver cracked the whip.</li><li>to break without complete separation of parts; break into fissures.</li><li>to break with a sudden, sharp sound: to crack walnuts.</li><li>to strike and thereby make a sharp noise: The boxer cracked his opponent on the jaw.</li><li>to induce or cause to be stricken with sorrow or emotion; affect deeply.</li><li>to utter or tell: to crack jokes.</li><li>to cause to make a cracking sound: to crack one's knuckles.</li><li>to damage, weaken, etc.: The new evidence against him cracked his composure.</li><li>to make mentally unsound.</li><li>to make (the voice) harsh or unmanageable.</li><li>to solve; decipher: to crack a murder case.</li><li>Informal: to break into (a safe, vault, etc.).</li><li>Chemistry: to subject to the process of cracking, as in the distillation of petroleum.</li><li>Informal: to open and drink (a bottle of wine, liquor, beer, etc.).</li></ul><p><strong>Noun</strong></p><ul><li>a break without complete separation of parts; fissure.</li><li>a slight opening, as between boards in a floor or wall, or between a door and its doorpost.</li><li>a sudden, sharp noise, as of something breaking.</li><li>the snap of or as of a whip.</li><li>a resounding blow: He received a terrific crack on the head when the branch fell.</li><li>Informal: a witty or cutting remark; wisecrack.</li><li>a break or change in the flow or tone of the voice.</li><li>Informal: opportunity; chance; try: Give him first crack at the new job.</li><li>a flaw or defect.</li><li>Also called rock: pellet-size pieces of highly purified cocaine, prepared with other ingredients for smoking, and known to be especially potent and addicting.</li><li>Masonry: check 1 (def 44).</li><li>a mental defect or deficiency.</li><li>a shot, as with a rifle: At the first crack, the deer fell.</li><li>a moment; instant: He was on his feet again in a crack.</li><li>Slang: a burglary, especially an instance of housebreaking.</li><li>Chiefly British: a person or thing that excels in some respect.</li><li>Slang: Vulgar; the vulva.</li><li>Chiefly Scot: conversation; chat.</li><li>British Dialect: boasting; braggadocio.</li><li>Archaic: a burglar.</li></ul><p><strong>Adjective</strong></p><ul><li>first-rate; excellent: a crack shot.</li></ul><p><strong>Adverb</strong></p><ul><li>with a cracking sound.</li></ul><p><strong>Verb Phrase</strong></p><ul><li>Nautical: (of a sailing vessel) to sail in high winds under sails that would normally be furled.</li><li>(of a power vessel) to advance at full speed in heavy weather.</li><li>to take severe or stern measures, especially in enforcing obedience to laws or regulations: The police are starting to crack down on local drug dealers.</li><li>Informal: to suffer a mental or emotional breakdown.</li><li>to crash, as in an automobile or airplane: He skidded into the telephone pole and cracked up.</li><li>to wreck an automobile, airplane, or other vehicle.</li><li>to laugh or to cause to laugh unrestrainedly: That story about the revolving door really cracked me up. Ed cracked up, too, when he heard it.</li><li>to cause (a piece of hot glass) to fall from a blowpipe or punty.</li></ul>