To asphyxiate someone is to stop them getting air, so they cannot breathe in a normal way — and, if it goes on, they die. Doctors, firefighters, and the police use this word more than ordinary people do. You can asphyxiate a person (smoke, a plastic bag, a hand on the throat), and a person can also asphyxiate: they stop breathing because there is no good air. The cause is often not “no air in the room” but air that cannot do its job — thick smoke, gas, or something blocking the mouth and nose. In everyday talk people often say suffocate instead; asphyxiate sounds more medical and more formal, the word you hear in a report, not in the kitchen. It is almost always about a body and breathing. People do sometimes stretch it (“asphyxiated by rules”), but that is literary, not how most speakers talk.

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