A boom is a very loud, deep sound that echoes. The distant boom of fireworks might spook your nervous dog.

Guns, thunder, drums, deep voices — all of these are capable of a pretty loud boom. When they make the sound, you can also say that they boom: "I saw the flash of lightning and got ready for the thunder to boom." Another kind of boom is a prosperous period, like an oil boom or an economic boom. The long pole that holds a microphone or the sail on a boat is yet another type of boom.

Definitions of boom
  1. noun
    a deep prolonged loud noise
    synonyms: roar, roaring, thunder
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    type of:
    sound of any kind (especially unintelligible or dissonant sound)
  2. verb
    make a deep hollow sound
    “Her voice booms out the words of the song”
    synonyms: boom out
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    type of:
    go, sound
    make a certain noise or sound
  3. verb
    make a resonant sound, like artillery
    “His deep voice boomed through the hall”
    synonyms: din
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    type of:
    go, sound
    make a certain noise or sound
  4. verb
    be the case that thunder is being heard
    synonyms: thunder
  5. verb
    hit hard
    synonyms: blast, nail, smash
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    type of:
    deal a blow to, either with the hand or with an instrument
  6. noun
    a sudden happening that brings good fortune (as a sudden opportunity to make money)
    “the demand for testing has created a boom for those unregulated laboratories where boxes of specimen jars are processed like an assembly line”
    synonyms: bonanza, bunce, godsend, gold rush, gravy, manna from heaven, windfall
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    type of:
    happening, natural event, occurrence, occurrent
    an event that happens
  7. noun
    a state of economic prosperity
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    type of:
    an economic state of growth with rising profits and full employment
  8. verb
    grow vigorously
    “business is booming
    synonyms: expand, flourish, thrive
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    be brought back to life, consciousness, or strength
    thrive profusely or flourish extensively
    type of:
    become larger, greater, or bigger; expand or gain
  9. noun
    any of various more-or-less horizontal spars or poles used to extend the foot of a sail or for handling cargo or in mooring
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    type of:
    a stout rounded pole of wood or metal used to support rigging
  10. noun
    a pole carrying an overhead microphone projected over a film or tv set
    synonyms: microphone boom
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    type of:
    a long (usually round) rod of wood or metal or plastic
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