Green’s Dictionary of Slang

1. (US) a positive endorsement, a piece of favourable publicity, thus dimin. boomlet.

1886		Nat. Police Gaz. (NY) 9 Oct. 2/3: ‘Miss’ Violet Cameron is advertised in a two-column article, and an extra-sensational ‘boom’ is effected for her by bringing her husband and her Lord ‘protector’ together over a gin fizz.
1889		‘’Arry in Switzerland’ in Punch 5 Dec. in P. Marks (2006) 98: The Bullanger boom was a fizzle. They say he’s mopped out; I dunnow.
1890		Music Hall & Theatre Rev. 8 Feb. 11/2: Another colossal company is the great ‘boom’ at the ‘Home of the Stars’.
1892		Advocate (Meridien, KS) 3 Feb. 9/1: Everyone understands that there is a gubernatorial boom now on, but [...] why the Republican press should think the fact that Mr Murdock was once a stone mason [...] is likely to help the book along.
1894		Mirror of Life 22 Sept. 9/4: When the manager tells stories / That are startling and prodigious / [...] / Do not mind him; ’tis a boomlet, / And it does not do.
1900		Marvel XIV:344 June 8: No better ‘boom’ could possibly have been given the three new music-hall stars.
1908		Sun. Times (Perth) 29 Nov. 4/8: We were rather afraid / Our boom wouldn’t be quite as big as the Butt’s.
1917		Wodehouse ‘The Making of Mac’s’ in Man with Two Left Feet 129: Hot stuff, kid. This is a jolly fine boom you’re working for the old place.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: boom. ‘Well in the boom’ to be popular where such popularity might lead to advancement in the ranks; regarded highly by one’s superior.
1925		S. Lewis Arrowsmith 375: He will do the big boom-boom and so bring us the credit in the newspapers.
1966		H.S. Thompson Hell’s Angels (1967) 95: There was no need to spoil a new boom for the film.

2. (Aus.) a success.

1889

Dead Bird (Sydney) 28 Sept. 5/4: Shakespeare is a big boom in Melbourne, and Miln is making money at a rapid rate.

3. (Aus.) a person, event or object that has been touted without possessing real quality.

1908

Sun (Kalgoorlie, WA) 6 Sept. 4/8: I am satisfied Burns is a kidder, / And Boshter, a boom, and a coot.

4. (Aus.) in sporting contexts, a favourite.

1910

Sun. Times (Perth) 17 Apr. 2nd sect. 10/4: Mallow has been a ‘boom’ on several occasions lately, but the son of Malvolio and Tottie has been weighed in the balances and found wanting.