Green’s Dictionary of Slang

1. a gross lie.

1936		(con. 1830s–60s) ‘Miles Franklin’ All That Swagger 148: ‘What a boomer!’ burst from Robert.
1955		N. Pulliam I Travelled a Lonely Land (1957) 230/2: boomer – [...] a big lie.

2. (Aus.) a large, powerful individual.

1843

Satirist & Sporting Chron. (Sydney) 11 Feb. 2/3: On stripping, we decidedly took the ‘boomer’ for choice, but the well-known [...] fighting character of the ‘little un’ left him many friends .

3. anything considered exceptionally large or strong.

1859		W. Burrows Adventures of a Mounted Trooper 90: The kangaroo [...] is the largest of all the wild animals; some full grown ‘old men’ or ‘boomers’.
1874		Hawaiian Gaz. 30 Sept. 4/3: No sportsman need be ashamed of a chase after a good ‘boomer’.
1885		Australasian Printers’ Keepsake 76: When the shades of evening come, / I choose a boomer of a gum.
1894		Truth (Sydney) 20 May. 1/1: The present Missing Word Competiton will be a boomer, inasmuch as there is already £161 3s in the pool.
1901		Bulletin (Sydney) 23 Nov. 14/4: Yes, had beastly luck. Got two real boomers nearly into the boat, and then lost ’em.
1908		Sun. Times (Perth) 29 Mar. 1/1: [of a baby show] The York boomer’s progenitors mean to sally along and snuff out the Northam nipper.
1910		Sun. Times (Perth) 30 Jan. 2nd sect. 7/1: The party bagging one dingo. 12 brace of ducks, 24 brush kangaroo and one ‘boomer’ .
1916		‘Anzac’ On the Anzac Trail 22: Our old hooker was just alive with cockroaches, too, and regular boomers they were; some as big as locusts.
1936		(con. 1830s–60s) ‘Miles Franklin’ All That Swagger 121: A hint without evidence is a snake in the grass, like that boomer you dispatched to-day at the lickhole.
1941		Baker Popular Dict. Aus. Sl. 12: Boomer, a particularly ambitious lie. Used loosely to denote anything large or noteworthy.
1942		Argus (Melbourne) 18 Apr. 3s/6: Stone the crows, buddy, is that a boomer! and how!
1956		J. Harvey ‘East Wind on Sunday’ in Drake-Brockman West Coast Stories (1959) 19: Gee, what a boomer! That’s my size!
1962		H.S. Thompson letter 1 Dec. in Proud Highway (1997) 358: Then to squat with the big boomer and feel it on my shoulder with the smell of grease and powder.
1970		D. Butts Down Under Up Close 30: Today’s ‘roos’ are smaller, but they are the world’s largest marsupial. A big ‘boomer’ is over six feet tall.
1982		J. Davis Dreamers 83: Sandy was as tough as an old boomer.
2021		P. Papathanasiou Stoning 83: [of a large kangaroo] ‘[T]his big red boomer bastard tore his whatchamacallit . . . oesophagus’.

4. something considered successful or popular.

1887		Courier-Journal (Louisville, KY) 30 Jan. 8/4: This sale will be a boomer for the very finest soft or stiff hat goes for $1.98 [DA].
1972		A. Chipper Aussie Swearers Guide 34: The opposite of a cow [...] is not bull, but often boomer or bottler, as in ‘a boomer of a day’.
1988		McGill Dict. of Kiwi Sl. 18/1: boomer something first-rate or successful, such as a topnotch surfing wave, but originally a large male kangaroo; eg ‘That paint job you did on the car, boomer, mate.’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].