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

MAD (măd)
Share:
abbr.
mutually assured destruction

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 
mad (măd)
Share:
adj. mad·der, mad·dest
1. Angry; resentful: was mad about the broken vase. See Synonyms at angry.
2.
a. Mentally deranged: "afflicted with hypochondria, depression, and fear of going mad" (Carla Cantor).
b. Characteristic of mental derangement: mad laughter.
c. Temporarily or apparently deranged by violent sensations, emotions, or ideas: was mad with jealousy.
3.
a. Lacking restraint or reason; foolish: I was mad to have hired her in the first place.
b. Feeling or showing strong liking or enthusiasm: mad about sports.
c. Marked by a lack of restraint, especially by extreme excitement, confusion, or agitation: a mad scramble for the bus.
4. Exhibiting uncharacteristic aggressiveness, especially as a result of rabies, spongiform encephalopathy, or another neurological disease. Used of animals: a mad dog; a mad cow.
5. Slang
a. Excellent; wonderful: It's really mad that they can come.
b. Abundant; great: mad respect.
tr. & intr.v. mad·ded, mad·ding, mads
To make or become mad; madden.
adv.
Slang
Extremely; very: This place is mad cool.
Idioms:
like mad Informal
1. Wildly; impetuously: drove like mad.
2. To an intense degree or great extent: worked like mad; snowing like mad.
mad as a hatter/March hare
Crazy; mentally deranged.

[Middle English, mentally deranged, rabid, angry, from Old English gemǣdde, past participle of *gemǣdan, to derange mentally, madden, from gemād, mentally deranged; see mei-1 in the Appendix of Indo-European roots.]

maddish adj.

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.