• synonyms


verb (used with object)
  1. to make flat.
  2. to knock down: The boxer flattened his opponent in the second round.
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verb (used without object)
  1. to become flat.
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Verb Phrases
  1. flatten in, Nautical. flat1(def 61).
  2. flatten out, Aeronautics. to fly into a horizontal position, as after a dive.
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Origin of flatten

First recorded in 1620–30; flat1 + -en1
Related formsflat·ten·er, nouno·ver·flat·ten, verb (used with object)un·flat·tened, adjective

Synonyms for flatten

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for unflattened

Historical Examples of unflattened

  • Their distance from the centre, compared with the radius of the unflattened circle, is called the excentricity.

    Pioneers of Science

    Oliver Lodge

  • His voice, deep and full for so young a child, inclined to unflattened vowels.

    The Higher Court

    Mary Stewart Daggett

British Dictionary definitions for unflattened


  1. (sometimes foll by out) to make or become flat or flatter
  2. (tr) informal
    1. to knock down or injure; prostrate
    2. to crush or subduefailure will flatten his self-esteem
  3. (tr) music to lower the pitch of (a note) by one chromatic semitoneUsual US word: flat
  4. (intr foll by out) to manoeuvre an aircraft into horizontal flight, esp after a dive
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Derived Formsflattener, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for unflattened



late 14c., "to prostrate oneself," also "to fall flat," from flat (adj.) + -en (1). Meaning "to make flat" is 1620s. Related: Flattened; flattening.

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Online Etymology Dictionary, © 2010 Douglas Harper