Green’s Dictionary of Slang

(orig. Aus./N.Z.) an excl. of approbation or assent.

1918		Kia Ora Coo-ee Aug. 5/2: ‘Fish for dinner to-day, Jack.’ ‘Good O! What sort?’ ‘Mafish.’.
1920		Advocate (Burnie, Tas.) 5 June 7/2: Good-oh, Snorkey — in with it — toot sweet ’ outski!
1928		Wodehouse ‘Compa y for Gertrude’ in Strand Sept. n.p.: ‘Good-oh!’ said Freddie. ‘Is the old doss-house very full up at the moment?’.
1928		A.W. Upfield House of Cain 264: ‘Goodo!’ replied Monty.
1928		A. Waugh Last Chukka 85: ‘Good-oh!’ she [an Australian] said, ‘that’ll be bonzer!’.
1938		X. Herbert Capricornia (1939) 32: Good-o, son. Just wait’ll I get the paint off.
1949		D. Walker We went to Aus. 193: Whatever you say to anyone it’s an even bet that they will counter with the cryptic remark ‘good-o’ [AND].
1949		R. Park Poor Man’s Orange 42: ‘Hughie! Hughie love,’ she bellowed through the closed door. ‘Good-oh,’ he answered surlily.
1951		D. Stivens Jimmy Brockett 34: ‘Will you let me help you pick the next one?’ ‘Good-oh,’ I said.
1957		A. Buckeridge Thanks to Jennings (1988) 98: You did! Goodo!
1958		(con. 1940s) B. Behan Borstal Boy 300: Good-oh. Geordie, reach me down a couple of pairs of overalls.
1960		‘Nino Culotta’ Cop This Lot 178: ‘You stickin’ with me?’ ‘Yes.’ ‘Goodo.’.
1961		R.S. Close With Hooves of Brass 136: ‘Good-oh, Pop! Come on, Eddie!’.
1973		(con. 1930s) F. Huelin ‘Keep Moving’ 4: ‘You can travel with me if you like.’ [...] ‘There’s nothing I’d like better,’ I replied. ‘Goodo!’ he said, proffering his hand.
2018		C. Hammer Scrublands [ebook] ‘Goodo. Piss off then!’.
2021		C. Hammer Opal Country 150: ‘Goodo. I want to access metadata from Stanley’s phone’.