off-gas noun 1verb 1forms 4 noun1 •Gas produced as a side effect of a chemical reaction, sometimes hazardous. verb1 •To emit gases, especially noxious ones.Since solvent-based paints can off-gas for a long time as they dry, when trapped in a tightly sealed building they can contribute to an unhealthy cocktail of chemicals in the air. — 2004 formsoff-gassed · off-gassing · off-gases · off-gasses