Fumes are a strong-smelling gas or smoke that you do not want in your lungs. You cannot usually see a neat cloud with a hard edge; you smell it, your eyes water, and after a while you feel sick or dizzy. Car exhaust in a closed garage, wet paint in a small room, petrol at a station, burning plastic, strong bleach — those are fumes. We nearly always say the word in the plural for this meaning: the fumes, paint fumes, petrol fumes (in American English, gasoline fumes). A little steam from soup is not fumes; fumes have a harsh, chemical, or burnt edge. People open windows, cover their mouths, or leave the room. Though actually, English also has the verb to fume, “to be quietly angry”, as if the anger were smoke coming off you — same old family of “smoke”, different job. For this entry, stay with the air you should not breathe.