verb (used with object)

to make flat.
to knock down: The boxer flattened his opponent in the second round.

verb (used without object)

to become flat.

Verb Phrases

flatten in, Nautical. flat1(def 61).
flatten out, Aeronautics. to fly into a horizontal position, as after a dive.

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. 2019

Examples from the Web for flatten

Contemporary Examples of flatten

  • He uses a spatula to flatten the onions and the meat together, creating a broad circular patty with an uneven edge.

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    The Most American Pit Stop in the U.S.A.

    Jane & Michael Stern

    July 21, 2014

  • They are specifically designed to ‘flatten out and mushroom’ when striking human tissue, and are intended to cause maximum damage.

  • In a way, the print emphasizes the pelt-like nature of all images, as they flatten out the world and hand it over to us.

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    Live Bear Is World's Biggest Paintbrush

    Blake Gopnik

    September 13, 2013

  • And, when Fajr-5s began making them run for cover they did not began shouting to "flatten all of Gaza."

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    "The Bubble" Bursting

    Orly Halpern

    November 21, 2012

  • Recessions tend to flatten income differentials, but this Great Recession is having the opposite effect.

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    Two Midsummer Fears

    David Frum

    July 27, 2012

Historical Examples of flatten

British Dictionary definitions for flatten



(sometimes foll by out) to make or become flat or flatter
(tr) informal
  1. to knock down or injure; prostrate
  2. to crush or subduefailure will flatten his self-esteem
(tr) music to lower the pitch of (a note) by one chromatic semitoneUsual US word: flat
(intr foll by out) to manoeuvre an aircraft into horizontal flight, esp after a dive
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 flatten

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

Online Etymology Dictionary, © 2010 Douglas Harper