Webster's Revised Unabridged Dictionary · 1913

Boomer

Boomer ({not transcribed}) , noun

1.
One who, or that which, booms.
2.
(Zoology) A North American rodent, so named because it is said to make a booming noise. See Sewellel.
3.
(Zoology) A large male kangaroo.
4.
One who works up a “boom”. [Slang, United States]