Green’s Dictionary of Slang

excellent, admirable, first-rate, esp. of racehorses.

1884		H. Smart Post to Finish I 111: We have got two clinking four-year-olds in the stable.
1885		Sheffield Wkly Teleg. 21 Mar. 3/3: ‘We’ve had a clinkin’ tea for ninepence apiece’.
1900		Bulletin (Sydney) 7 Apr. 24/1: Patterson proved cold pie for the bantam premier in the next term, and was sent sleeping by a clinking right on the point.
1936		N. Gale ‘Safety First’ in Close of Play 25: Be dead to office rule, / And, rolling roycily along / The tarmac, hum that clinking song / You learnt at Harrow School!