adjective, flat·ter, flat·test.

  1. horizontally level: a flat roof.
  2. level, even, or without unevenness of surface, as land or tabletops.
  3. having a surface that is without marked projections or depressions: a broad, flat face.
  4. lying horizontally and at full length, as a person; prostrate: He was flat on the canvas after the knockdown.
  5. lying wholly on or against something: The banner was flat against the wall.
  6. thrown down, laid low, or level with the ground, as fallen trees or buildings.
  7. having a generally level shape or appearance; not deep or thick: a flat plate.
  8. (of the heel of a shoe) low and broad.
  9. spread out, as an unrolled map or the open hand.
  10. deflated; collapsed: a flat tire.
  11. absolute, downright, or positive; without qualification: a flat denial.
  12. without modification or variation: a flat rate.
  13. Informal. lacking money; broke.
  14. without vitality or animation; lifeless; dull: flat writing.
  15. having lost its flavor, sharpness, or life, as wine or food; stale.
  16. (of a beverage) having lost its effervescence.
  17. without flavor; not spiced: flat cooking.
  18. prosaic, banal, or insipid: a flat style.
  19. pointless, as a remark or joke.
  20. commercially inactive: a flat day in the stock market.
  21. (of a painting) not having the illusion of volume or depth.
  22. (of a photograph or painting) lacking contrast or gradations of tone or color.
  23. (of paint) without gloss; not shiny; mat.
  24. not clear, sharp, or ringing, as sound or a voice.
  25. lacking resonance and variation in pitch; monotonous: a flat delivery of the speech.
  26. Music.
    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).
  27. 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.
  28. Phonetics. lenis; voiced.
  29. Nautical. (of a sail)
    1. cut with little or no fullness.
    2. trimmed as nearly fore-and-aft as possible, for sailing to windward.
  30. flat a, the a-sound (a) of glad, bat, or act.


  1. something flat.
  2. a shoe, especially a woman’s shoe, with a flat heel or no heel.
  3. a flat surface, side, or part of anything: He struck me with the flat of his hand.
  4. flat or level ground; a flat area: salt flats.
  5. a marsh, shoal, or shallow.
  6. Music.
    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.
  7. Theater. a piece of scenery consisting of a wooden frame, usually rectangular, covered with lightweight board or fabric.
  8. a broad, thin book, chiefly for children: a juvenile flat.
  9. Informal. a deflated automobile tire.
  10. (in postal use) a large flat package, as in a manila envelope, for mailing.
  11. Architecture. a flat roof or deck.
  12. Nautical.
    1. Also called platform.a partial deck between two full decks.
    2. a low, flat barge or lighter.
  13. Shipbuilding.
    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.
  14. an iron or steel bar of rectangular cross section.
  15. Textiles. one of a series of laths covered with card clothing, used in conjunction with the cylinder in carding.
  16. Photography. one or more negatives or positives in position to be reproduced.
  17. Printing. a device for holding a negative or positive flat for reproduction by photoengraving.
  18. Horticulture. a shallow, lidless box or tray used for rooting seeds and cuttings and for growing young plants.
  19. a similar box used for shipping and selling fruits and vegetables.
  20. Football. the area of the field immediately inside of or outside of an offensive end, close behind or at the line of scrimmage.
  21. flats, Informal. flat races between horses.Compare flat race.

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

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

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

  1. to become flat.


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

Verb Phrases

  1. flat in, Nautical. to pull the clew of (a fore-and-aft sail) as nearly amidships as possible.Also flatten in.
  1. fall flat, to fail to produce the desired effect; fail completely: His attempts at humor fell flat.
  2. flat aft, Nautical. trimmed so that fore-and-aft sails present as flat a surface as possible, as in sailing close to the wind.
  3. flat on one’s back. back1(def 47).
  4. 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.


  1. Chiefly British. an apartment or suite of rooms on one floor forming a residence.

adjective flatter or flattest

  1. horizontal; levelflat ground; a flat roof
  2. even or smooth, without projections or depressionsa flat surface
  3. lying stretched out at full length; prostratehe lay flat on the ground
  4. having little depth or thickness; shallowa flat dish
  5. (postpositive often foll by against) having a surface or side in complete contact with another surfaceflat against the wall
  6. spread out, unrolled, or levelled
  7. (of a tyre) deflated, either partially or completely
  8. (of shoes) having an unraised or only slightly raised heel
  9. 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
  10. without qualification; totala flat denial
  11. without possibility of change; fixeda flat rate
  12. (prenominal or immediately postpositive) neither more nor less; exacthe did the journey in thirty minutes flat; a flat thirty minutes
  13. unexciting or lacking point or interesta flat joke
  14. without variation or resonance; monotonousa flat voice
  15. (of food) stale or tasteless
  16. (of beer, sparkling wines, etc) having lost effervescence, as by exposure to air
  17. (of trade, business, a market, etc) commercially inactive; sluggish
  18. (of a battery) fully discharged; dead
  19. (of a print, photograph, or painting) lacking contrast or shading between tones
  20. (of paint) without gloss or lustre; matt
  21. (of a painting) lacking perspective
  22. (of lighting) diffuse
  23. music
    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)
  24. phonetics another word for lenis
  25. 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)


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


  1. a flat object, surface, or part
  2. (often plural) a low-lying tract of land, esp a marsh or swamp
  3. (often plural) a mud bank exposed at low tide
  4. music
    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)
  5. theatre a rectangular wooden frame covered with painted canvas, etc, used to form part of a stage setting
  6. a punctured car tyre
  7. the flat mainly British ((often cap.))
    1. flat racing, esp as opposed to steeplechasing and hurdling
    2. the season of flat racing
  8. nautical a flatboat or lighter
  9. US and Canadian a shallow box or container, used for holding plants, growing seedlings, etc

verb flats, flatting or flatted

  1. to make or become flat
  2. music the usual US word for flatten (def. 3)


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

verb flats, flatting or flatted (intr)

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

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.).

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
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