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.

Nearby words

  1. flatmate,
  2. flatness,
  3. flats,
  4. flatscreen,
  5. flatstick,
  6. flatter,
  7. flatter oneself,
  8. flattered,
  9. flatterer,
  10. flattering

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

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for 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