Gas  —n. (pl. -es) 1 any airlike substance (i.e. Not solid or liquid) moving freely to fill any space available. 2 such a substance (esp. Found naturally or extracted from coal) used as fuel (also attrib.: gas cooker; gas industry). 3 nitrous oxide or other gas as an anaesthetic. 4 poisonous gas used in war. 5 us colloq. Petrol, gasoline. 6 slang idle talk; boasting. 7 slang enjoyable or amusing thing or person. —v. (gases, gassed, gassing) 1 expose to gas, esp. To kill. 2 colloq. Talk idly or boastfully.