Green’s Dictionary of Slang

(orig. US) excellently, wonderfully.

1908		S.E. White Riverman 323: ‘She’s holding strong and dandy,’ said Orde [...] examining critically the clumps of piles.
1928		F. Willard ‘Moon Mullins’ [comic strip] That suits me just dandy.
1933		Ramona Davies ‘Are You Making Any Money?’ 🎵 You make time, and you make love dandy, / You make swell molasses candy, / But, honey, are you making any money, / That’s all I want to know!
1952		(con. 1944) Wilder & Blum Stalag 17 [film script] 51: Harry and Stosh are doing dandy.
1956		N. Algren Walk on the Wild Side 136: He had a big bad head and held it hard, mourning ‘Oh, it drinked dandy but Lord the afterwards’.
1966		Sun. Times 5 June n.p.: Jeez, I’m so glad you was along, that worked out just dandy.