I read Sam Knight’s article about “Ronnie O’Sullivan, snooker’s greatest player” despite knowing nothing about snooker because (as often happens with the New Yorker) it was so well written it hooked me. (There’s also a great video to accompany it.) When I recommended it to my wife, I said it was about /ˈsnuːkər/, with long oo as in moot, and she said “Isn’t it /ˈsnukər/?” with short oo as in book. I looked it up in M-W and the AHD and said “You’re right, I wonder how I came up with the long-oo pronunciation?” Then I looked it up in the OED and discovered I must have heard a Brit say it, because /ˈsnuːkə(r)/ is the UK pronunciation. This must be one of the lesser-known transatlantic shibboleths; US dictionaries don’t mention the UK version, and vice versa (though I see Wikipedia gives both). I’m not sure how the US developed its own variant, since the game was invented by British Army officers less than 150 years ago and I don’t think has ever been popular in the US, though I speak under correction.
The etymology is unknown; the OED, in a century-old article, says:
Etymology: Of obscure origin.
It is commonly held that the word represents an allusive use of snooker n.1 a newly joined cadet, first applied to the game by Col. Sir Neville Chamberlain (1856–1944), a subaltern in the Devonshire Regiment stationed at Jabalpur in central India in 1875, with reference to the rawness of the play of a fellow officer. The story is often repeated, e.g. in The Times (1980) 29 Dec. 9.