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



adjective, flat·ter, flat·test.

horizontally level: a flat roof.
level, even, or without unevenness of surface, as land or tabletops.
having a surface that is without marked projections or depressions: a broad, flat face.
lying horizontally and at full length, as a person; prostrate: He was flat on the canvas after the knockdown.
lying wholly on or against something: The banner was flat against the wall.
thrown down, laid low, or level with the ground, as fallen trees or buildings.
having a generally level shape or appearance; not deep or thick: a flat plate.
(of the heel of a shoe) low and broad.
spread out, as an unrolled map or the open hand.
deflated; collapsed: a flat tire.
absolute, downright, or positive; without qualification: a flat denial.
without modification or variation: a flat rate.
Informal. lacking money; broke.
without vitality or animation; lifeless; dull: flat writing.
having lost its flavor, sharpness, or life, as wine or food; stale.
(of a beverage) having lost its effervescence.
without flavor; not spiced: flat cooking.
prosaic, banal, or insipid: a flat style.
pointless, as a remark or joke.
commercially inactive: a flat day in the stock market.
(of a painting) not having the illusion of volume or depth.
(of a photograph or painting) lacking contrast or gradations of tone or color.
(of paint) without gloss; not shiny; mat.
not clear, sharp, or ringing, as sound or a voice.
lacking resonance and variation in pitch; monotonous: a flat delivery of the speech.
  1. (of a tone) lowered a half step in pitch: B flat.
  2. below an intended pitch, as a note; too low (opposed to sharp).
Grammar. derived without change in form, as English to brush from the noun brush and adverbs that do not add -ly to the adjective form as fast, cheap, and slow.
Phonetics. lenis; voiced.
Nautical. (of a sail)
  1. cut with little or no fullness.
  2. trimmed as nearly fore-and-aft as possible, for sailing to windward.
flat a, the a-sound (a) of glad, bat, or act.


something flat.
a shoe, especially a woman's shoe, with a flat heel or no heel.
a flat surface, side, or part of anything: He struck me with the flat of his hand.
flat or level ground; a flat area: salt flats.
a marsh, shoal, or shallow.
  1. (in musical notation) the character ♭, which when attached to a note or to a staff degree lowers its significance one chromatic half step.
  2. a tone one chromatic half step below another: The flat of B is B flat.
  3. (on keyboard instruments, with reference to any given note) the key next below or to the left.
Theater. a piece of scenery consisting of a wooden frame, usually rectangular, covered with lightweight board or fabric.
a broad, thin book, chiefly for children: a juvenile flat.
Informal. a deflated automobile tire.
(in postal use) a large flat package, as in a manila envelope, for mailing.
Architecture. a flat roof or deck.
  1. Also called platform.a partial deck between two full decks.
  2. a low, flat barge or lighter.
  1. a broad, flat piece of iron or steel for overlapping and joining two plates at their edges.
  2. a straight timber in a frame or other assembly of generally curved timbers.
an iron or steel bar of rectangular cross section.
Textiles. one of a series of laths covered with card clothing, used in conjunction with the cylinder in carding.
Photography. one or more negatives or positives in position to be reproduced.
Printing. a device for holding a negative or positive flat for reproduction by photoengraving.
Horticulture. a shallow, lidless box or tray used for rooting seeds and cuttings and for growing young plants.
a similar box used for shipping and selling fruits and vegetables.
Football. the area of the field immediately inside of or outside of an offensive end, close behind or at the line of scrimmage.
flats, Informal. flat races between horses.Compare flat race.

verb (used with object), flat·ted, flat·ting.

to make flat.
Music. to lower (a pitch), especially one half step.

verb (used without object), flat·ted, flat·ting.

to become flat.


in a flat position; horizontally; levelly.
in a flat manner; positively; absolutely.
completely; utterly: flat broke.
exactly; precisely: She ran around the track in two minutes flat.
Music. below the true pitch: to sing flat.
Finance. without interest.

Verb Phrases

flat in, Nautical. to pull the clew of (a fore-and-aft sail) as nearly amidships as possible.Also flatten in.


    fall flat, to fail to produce the desired effect; fail completely: His attempts at humor fell flat.
    flat aft, Nautical. trimmed so that fore-and-aft sails present as flat a surface as possible, as in sailing close to the wind.
    flat on one's back. back1(def 47).
    flat out, Informal.
    1. without hesitation; directly or openly: He told us flat out he'd been a double agent.
    2. at full speed or with maximum effort.

Origin of flat

1275–1325; Middle English < Old Norse flatr, akin to Old English flet (see flat2), Greek platýs (see platy-, plate1
Related formsflat·ly, adverbflat·ness, nounun·flat·ted, adjective

Synonyms for flat

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

Antonyms for flat

1, 4. upright, vertical. 14. spirited. 17. savory.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for flat out

directly, openly, bluntly, full-bore

British Dictionary definitions for flat out



adjective flatter or flattest

horizontal; levelflat ground; a flat roof
even or smooth, without projections or depressionsa flat surface
lying stretched out at full length; prostratehe lay flat on the ground
having little depth or thickness; shallowa flat dish
(postpositive often foll by against) having a surface or side in complete contact with another surfaceflat against the wall
spread out, unrolled, or levelled
(of a tyre) deflated, either partially or completely
(of shoes) having an unraised or only slightly raised heel
mainly British
  1. (of races, racetracks, or racecourses) not having obstacles to be jumped
  2. of, relating to, or connected with flat racing as opposed to steeplechasing and hurdlingflat jockeys earn more
without qualification; totala flat denial
without possibility of change; fixeda flat rate
(prenominal or immediately postpositive) neither more nor less; exacthe did the journey in thirty minutes flat; a flat thirty minutes
unexciting or lacking point or interesta flat joke
without variation or resonance; monotonousa flat voice
(of food) stale or tasteless
(of beer, sparkling wines, etc) having lost effervescence, as by exposure to air
(of trade, business, a market, etc) commercially inactive; sluggish
(of a battery) fully discharged; dead
(of a print, photograph, or painting) lacking contrast or shading between tones
(of paint) without gloss or lustre; matt
(of a painting) lacking perspective
(of lighting) diffuse
  1. (immediately postpositive)denoting a note of a given letter name (or the sound it represents) that has been lowered in pitch by one chromatic semitoneB flat
  2. (of an instrument, voice, etc) out of tune by being too low in pitchCompare sharp (def. 12)
phonetics another word for lenis
flat a phonetics the vowel sound of a as in the usual US or S Brit pronunciation of hand, cat, usually represented by the symbol (æ)


in or into a prostrate, level, or flat state or positionhe held his hand out flat
completely or utterly; absolutelyhe went flat against the rules
exactly; preciselyin three minutes flat
  1. lower than a standard pitch
  2. too low in pitchshe sings flat Compare sharp (def. 18)
fall flat to fail to achieve a desired effect, etc
flat out informal
  1. with the maximum speed or effort
  2. totally exhausted


a flat object, surface, or part
(often plural) a low-lying tract of land, esp a marsh or swamp
(often plural) a mud bank exposed at low tide
  1. an accidental that lowers the pitch of the following note by one chromatic semitoneUsual symbol:
  2. a note affected by this accidentalCompare sharp (def. 19)
theatre a rectangular wooden frame covered with painted canvas, etc, used to form part of a stage setting
a punctured car tyre
the flat mainly British ((often cap.))
  1. flat racing, esp as opposed to steeplechasing and hurdling
  2. the season of flat racing
nautical a flatboat or lighter
US and Canadian a shallow box or container, used for holding plants, growing seedlings, etc

verb flats, flatting or flatted

to make or become flat
music the usual US word for flatten (def. 3)
See also flats
Derived Formsflatly, adverbflatness, noun

Word Origin for flat

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




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

Word Origin and History for flat out



early 14c., from Old Norse flatr, from Proto-Germanic *flataz (cf. Old Saxon flat "flat, shallow,: Old High German flaz "flat, level," Old English flet, Old High German flezzi "floor"), perhaps from PIE *plat- "to spread" (cf. Greek platys "broad, flat;" see plaice (n.)).

Sense of "prosaic, dull" is from 1570s; used of drink from c.1600; of musical notes from 1590s, because the tone is "lowered." Flat-out (adv.) "openly, directly" is from 1932; earlier it was a noun meaning "total failure" (1870, U.S. colloquial).



1801, from Scottish flat "floor or story of a house," from Old English flet "a dwelling, floor, ground," from the same source as flat (adj.).

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with flat out

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]


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.