To deafen means to make someone unable to hear, either temporarily or permanently. A sudden, extremely loud noise like an explosion can deafen people nearby, damaging the delicate parts inside their ears that detect sound. Rock musicians who perform without ear protection sometimes become partially deafened over years of exposure to amplified music.

More commonly, people use deafen to describe sounds so loud they temporarily overwhelm your hearing. After a fire alarm goes off right next to you, you might say it nearly deafened you. The roar of jet engines at an airport can be deafening. When something is deafening, it's so loud that for a few moments you can't hear anything else, and your ears might ring afterward.

The word can also describe overwhelming noise itself. If your whole class starts shouting at once, the deafening chaos makes it impossible for your teacher to hear anyone's individual voice. Notice that deafening is different from simply loud: it suggests noise so intense it interferes with your ability to hear.