The act of sending out something, such as gas, light, heat, or sound. It often refers to gases released into the air, especially from cars and factories.
From Latin 'emissio' (a sending out), from 'emittere' (to send out), from 'e-' (out) + 'mittere' (to send). English adopted it for physical and later technical contexts. The environmental meaning about pollution became especially prominent in the 20th century.
The word 'emission' is neutral—anything can be emitted—but modern life has made it almost a synonym for 'pollution.' That shift shows how strongly climate and air quality dominate our thinking now. The same root gives us 'mission' and 'missile,' all about things being sent out into the world.
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