Definition of "boomer"

boomer¹

/ˈbuːmə(ɹ)/

noun
plural boomers
1. An adult male kangaroo.
2. Something that makes a booming sound.
  Quotations
  That's when the Rev let loose one of those great big boomers of a laugh. It was so loud in the closed space, the effect was what Wes imagined it felt like to hear a bullet fired in a car.
  2010, Pearl Cleage, Till You Hear from Me, page 151
3. (US, mainly 1920–1930) A transient worker who would move from boom town to boom town in search of temporary work.
4. A device used to bind or tighten chain.
5. (US, nautical, military, slang) A nuclear ballistic missile submarine, SSBN.
  Quotations
  Distant contact, probably submerged. It's a wild guess, but I'd say we hit a boomer coming out of the barn. Could be a missile boat out of Polijarny.
  1990, The Hunt For Red October
6. (UK) A bittern (subfamily Botaurinae).
7. (Appalachia) A red squirrel (Tamiasciurus hudsonicus).
8. A mountain beaver (Aplodontia rufa).
9. (US, historical) Alternative letter-case form of Boomer (“Oklahoma settler”)

boomer²

/ˈbuːmə(ɹ)/

noun
plural boomers
1. (informal) Ellipsis of baby boomer.
  Quotations
  To the many Boomers who sensed that something had gone awry in Greatest Generation America, Mad was a glimmer of truth, a benign but trenchant voice against hypocrisy and pretense, a way to laugh at parents who fretted over status symbols and authorities who talked one way but acted another.
  2007, Leonard Steinhorn, The Greater Generation: In Defense of the Baby Boom Legacy, New York: Macmillan
  These fears have been exacerbated by the recession, which forced many boomers to turn to Social Security earlier than anticipated because of long-term unemployment and financial crises (Johnson and Wilson, 2010a, b).
  2015, Melvin Delgado, Baby Boomers of Color […] , page 4
2. (by extension, slang, sometimes derogatory) An elderly person, regardless of generation.
3. (by extension, slang, sometimes derogatory) A person who is too old to be familiar with the use of recent technology.