Green’s Dictionary of Slang

1. of objects or people, enjoyable, exciting, funny.

1904		C. Connors Bowery Life [ebook] ‘Extract of what?’ asked de wise guy, showing his crockery wid a gas laugh.
1946		D. MacDonagh Happy as Larry Act I: She’s a gas looking widow all right.
1950		B. Behan After the Wake (1981) 54: The gassest little ex-Dublin Fusilier in the street.
1955		J.P. Donleavy Ginger Man (1958) 181: You’re a gas man.
1966		P. Boyle At Night All Cats Are Grey 124: It’ll be right gas. [Ibid.] 162: He’s a gas man, the bould Willie.
1987		(con. 1920s) L. Redmond Emerald Square 95: You’re a gas man.
1991		R. Doyle The Van (1998) 404: He was some tulip, Bertie; he was fuckin’ gas.
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Gas (a): funny.
2021		L. McInerney Rules of Revelation 293: ‘You weren’t Tara’s young wan?’ he said. ‘I am.’ ‘Isn’t that gas? You don’t look much like her’.

2. impressive, extraordinary.

1961		Rigney & Smith Real Bohemia xiv: gas the best, the most.
1990		R. Doyle Snapper 139: Michah’s ma ate coal when she was havin’ him. [...] That’s gas.
2005		P. Howard Curious Incident of the Dog in the Nightdress 259: I had a chat with oul’ Fehily. A gas character altogether.
2021		P Howard Braywatch 14: ‘Look at him swimming there, he’s gas!’.

3. see gassy adj.¹ (2)