a blemish resulting from a break without complete separation of the parts
"there was a crack in the mirror"
a purified and potent form of cocaine that is smoked rather than snorted; highly addictive
"He tried to resist the urge to smoke crack again after his last relapse had nearly destroyed everything he owned."
A thin and usually jagged space opened in a previously solid material.
"A hairline crack appeared across the screen after I dropped my phone on the concrete."
In plain English: A crack is a small break or split in something solid, like a piece of glass or a wall.
"The old window had a small crack in the glass."
Usage: Use the noun "crack" to describe a narrow opening or fissure that forms in a solid object, such as glass, ice, or dry earth. You might say there is a crack in the windowpane when referring to this physical break.
hit forcefully; deal a hard blow, making a cracking noise
"The teacher cracked him across the face with a ruler"
pass through (a barrier)
"Registrations cracked through the 30,000 mark in the county"
gain unauthorized access computers with malicious intentions
"she cracked my password"
"crack a safe"
reduce (petroleum) to a simpler compound by cracking
"The refinery increased its output of gasoline by running more crude oil through the crackers at higher temperatures."
To form cracks.
"The old wooden fence began to crack under the relentless heat of the summer sun."
In plain English: To crack something means to break it with a loud noise, usually by hitting it hard.
"She cracked an egg into the bowl to start making pancakes."
Usage: Use "crack" when something breaks slightly or develops fissures under pressure, such as an eggshell splitting or ice forming lines on a frozen lake. Avoid using it to describe a loud noise unless that sound results directly from the material breaking apart.
Highly trained and competent.
"The team was led by a crack squad of investigators who solved the case in hours."
In plain English: Crack describes something that is broken, damaged, or split into pieces.
"The cracked screen on my phone makes it hard to see during the day."
Usage: Do not use "crack" as an adjective to mean highly trained or competent; this is a common error because it misinterprets the word's slang usage for a skilled person (a noun) as a descriptive term. Instead, reserve "crack" for describing sounds like breaking noises or referring to someone as a "crack" specialist only when using it in its specific noun form within phrases like "a crack team."
The word "crack" comes from Old English cracian, which originally meant to resound or make a cracking noise. It traveled into modern English through Middle English while retaining its core meaning of making a sharp sound.