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90s Slang You Should Know


[flat-n] /ˈflæt n/
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 forms
flattener, noun
overflatten, verb (used with object)
unflattened, adjective
2. ground, fell, prostrate, deck, floor. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for flatten
Contemporary Examples
Historical Examples
  • He meant to flatten out a hundred feet or so above them and shout, "For I'm a rider of the sky!"

    Skyrider B. M. Bower
  • Raise tacks and sheets, round with the main-yard, and flatten in forward.

    The Voyage of the Aurora Harry Collingwood
  • They had just time to flatten themselves against the crag, which, fortunately, hung over them.

    The Spell of Switzerland Nathan Haskell Dole
  • You could flatten out a piece of iron with your little lady-like arms.

    L'Assommoir Emile Zola
  • Cut another stick (H) an inch through and fifteen inches long, flatten a little on one side.

    Deadfalls and Snares A. R. (Arthur Robert) Harding
British Dictionary definitions for flatten


(sometimes foll by out) to make or become flat or flatter
(transitive) (informal)
  1. to knock down or injure; prostrate
  2. to crush or subdue: failure will flatten his self-esteem
(transitive) (music) to lower the pitch of (a note) by one chromatic semitone Usual US word flat
(intransitive) foll by out. to manoeuvre an aircraft into horizontal flight, esp after a dive
Derived Forms
flattener, 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
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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
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