[ flat-out ]
/ ˈflætˈaʊt /

adjective Informal.

moving or working at top speed or with maximum effort; all-out: a flat-out effort by all contestants.
downright; thoroughgoing: Many of the paintings were flat-out forgeries.

Origin of flat-out

First recorded in 1925–30

Definition for flat out (2 of 2)

Origin of flat

1275–1325; Middle English < Old Norse flatr, akin to Old English flet (see flat2), Greek platýs (see platy-, plate1


1 plane. See level.
4 low, prone.
11 outright, peremptory, categorical.
14 boring, spiritless, prosaic.
17 vapid, unsavory.


flat·ly, adverbflat·ness, nounun·flat·ted, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for flat out (1 of 2)

See also flats

Derived forms of flat

flatly, adverbflatness, noun

Word Origin for flat

C14: from Old Norse flatr; related to Old High German flaz flat, Greek platus flat, broad

British Dictionary definitions for flat out (2 of 2)

/ (flæt) /


a set of rooms comprising a residence entirely on one floor of a buildingUsual US and Canadian name: apartment
British and NZ a portion of a house used as separate living quarters
NZ a house shared with people who are not members of one's own family

verb flats, flatting or flatted (intr)

Australian and NZ to live in a flat (with someone)

Word Origin for flat

Old English flett floor, hall, house; related to flat 1
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

Idioms and Phrases with flat out (1 of 2)

flat out


In a direct manner, bluntly. For example, He told the true story flat out. [Colloquial; mid-1900s]


At top speed, as in She was running flat out to catch the train. [Slang; c. 1930]

Idioms and Phrases with flat out (2 of 2)


In addition to the idioms beginning with flat

  • flat as a pancake
  • flat broke
  • flat on one's back
  • flat out

also see:

  • caught flat-footed
  • fall flat
  • in no time (nothing flat)
  • leave flat
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.