crack
n. countablen. a thin line on the surface of something that is broken but not completely separated. You might see a crack in a wall, a phone screen, or a plate.
n. a narrow fissure or opening on the surface of an object, indicating a partial break or fracture without complete separation of the parts.
There is a small crack in the window.
After the earthquake, he found a long crack running up the wall of his living room.
The antique vase was almost perfect, its value diminished only by a hairline crack near the base, visible only upon close inspection.
From Middle English crakken, craken, from Old English cracian (“to resound, crack”), from Proto-West Germanic krakōn, from Proto-Germanic krakōną (“to crack, crackle, shriek”), ultimately from Proto-Indo-European *gerh₂- (“to resound, cry hoarsely”). Cognate with Scots crak (“to crack”), West Frisian kreakje (“to crack”), Dutch kraken (“to crunch, creak, squeak”), Low German kraken (“to crack”), German krachen (“to crash, crack, creak”), Lithuanian gi̇̀rgžděti (“to creak, squeak”), Old Armenian կարկաչ (karkačʻ), Sanskrit गर्जति (gárjati, “to roar, hum”). Compare typologically English crevice (<< Latin crepō), Bulgarian пукнатина (puknatina) (akin to пу́кам (púkam)), Russian тре́щина (tréščina) (akin to треск (tresk)), щель (ščelʹ) (akin to щёлкать (ščólkatʹ)).
Slang first attested 1793, perhaps from the verb in the sense of doing something quickly or with intelligence, or in the sense of "speaking boastingly" and having something to be proud of.