crackcrackcrackscrackedcracking1verb (cracks, cracking, cracked)1to break, but not into separate pieces: The glass will crack if you pour boiling water into it.This cup is cracked.2to make a sudden loud noisecrack down on somebody or somethingto become stricter when dealing with bad or illegal behaviour: The police are cracking down on drug dealers.crackcrackcrackscrackedcracking2noun1a thin line on something where it has broken, but not into separate pieces: There's a crack in this glass.2a narrow space between two things or two parts of something: a crack in the curtains3a sudden loud noise: a crack of thunder