use-icon

HOW TO USE THE DICTIONARY

To look up an entry in The American Heritage Dictionary of the English Language, use the search window above. For best results, after typing in the word, click on the “Search” button instead of using the “enter” key.

Some compound words (like bus rapid transit, dog whistle, or identity theft) don’t appear on the drop-down list when you type them in the search bar. For best results with compound words, place a quotation mark before the compound word in the search window.

guide to the dictionary

use-icon

THE USAGE PANEL

The Usage Panel is a group of nearly 200 prominent scholars, creative writers, journalists, diplomats, and others in occupations requiring mastery of language. Annual surveys have gauged the acceptability of particular usages and grammatical constructions.

The Panelists

open-icon

AMERICAN HERITAGE DICTIONARY APP

The new American Heritage Dictionary app is now available for iOS and Android.

scroll-icon

THE AMERICAN HERITAGE DICTIONARY BLOG

The articles in our blog examine new words, revised definitions, interesting images from the fifth edition, discussions of usage, and more.

100-words-icon

See word lists from the best-selling 100 Words Series!

Find out more!

open-icon

INTERESTED IN DICTIONARIES?

Check out the Dictionary Society of North America at http://www.dictionarysociety.com

flat 1 (flăt)
Share:
adj. flat·ter, flat·test
1.
a. Having a smooth, even surface: a flat field. See Synonyms at level.
b. Having a relatively broad level surface in relation to thickness or depth: a flat box.
2.
a. Being in horizontal position; lying down: flat on his back.
b. Being without slope or curvature: a flat line on a chart.
c. Having a low heel or no heel: flat shoes.
3. Free of qualification; absolute: a flat refusal.
4. Fixed; unvarying: a flat rate.
5. Lacking interest or excitement; dull: a flat scenario.
6.
a. Lacking in flavor: a flat stew that needs salt.
b. Having lost effervescence or sparkle: flat beer.
7.
a. Deflated. Used of a tire.
b. Electrically discharged. Used of a storage battery.
8. Of or relating to a horizontal line that displays no ups or downs and signifies the absence of physiological activity: A flat electroencephalogram indicates a loss of brain function.
9. Of or relating to a hierarchy with relatively few tiers or levels: a flat organization chart.
10. Commercially inactive; sluggish: flat sales for the month.
11. Unmodulated; monotonous: a flat voice.
12. Lacking variety in tint or shading; uniform: "The sky was bright but flat, the color of oyster shells" (Anne Tyler).
13. Not glossy; matte: flat paint.
14. Music
a. Being below the correct pitch.
b. Being one half step lower than the corresponding natural key: the key of B flat.
15. Designating the vowel a as pronounced in bad or cat.
16. Nautical Taut. Used of a sail.
17. Informal Having small breasts.
adv.
1.
a. Level with the ground; horizontally.
b. On or up against a flat surface; at full length.
2. So as to be flat.
3.
a. Directly; completely: went flat against the rules; flat broke.
b. Exactly; precisely: arrived in six minutes flat.
4. Music Below the intended pitch.
5. Business Without interest charge.
n.
1. A flat surface or part.
2. often flats A stretch of level ground: salt flats.
3. A shallow frame or box for seeds or seedlings.
4. A movable section of stage scenery, usually consisting of a wooden frame and a decorated panel of wood or cloth.
5. A flatcar.
6. A deflated tire.
7. A shoe with a flat heel.
8. A large flat piece of mail.
9. A horse that competes in a flat race. Also called runner.
10. Music
a. A sign (♭) used to indicate that a note is to be lowered by a semitone.
b. A note that is lowered a semitone.
11. Football The area of the field to either side of an offensive formation.
v. flat·ted, flat·ting, flats
v.tr.
1. To make flat; flatten.
2. Music To lower (a note) a semitone.
v.intr.
Music
To sing or play below the proper pitch.
[Middle English, from Old Norse flatr; see plat- in the Appendix of Indo-European roots.]
flatly adv.
flatness n.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 
flat 2 (flăt)
Share:
n.
1. An apartment on one floor of a building.
2. Archaic A story in a house.
[Alteration of Scots flet, inner part of a house, from Middle English, from Old English, floor, dwelling; see plat- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

American Heritage Dictionary Products