Green’s Dictionary of Slang

(US) very well, excellently, kindly.

1856		S. Butler letter 22 Mar. in Corresp. (1962) 55: Snow did very badly in the History paper and is said to have lost two places by it; a very likely thing for his principal antagonist did awfully swell in it .
1860		Belfast Morn. News 6 Aug. 4/1: I was got up swell.
1895		Times (Richmond, VA) 6 Oct. 15/6: The ‘source’ of his madness nobody could tell; / But they guessed it was caused by him living too swell.
1910		H. Hapgood Types from City Streets 310: If a pal’s got it, and wants to be buried swell, we remember it if he’s been a good guy.
1921		Dos Passos Three Soldiers 12: ‘Gee, she used to cook swell,’ he murmured regretfully.
1937		E. Anderson Thieves Like Us (1999) 178: Plenty of fellows have gone down there and liked it swell.
1948		Z.N. Hurston Seraph on the Suwanee (1995) 814: He liked Kenny’s piece a lot. It was rhumba and it went over swell.
1952		Lait & Mortimer USA Confidential 127: That worked out swell.