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rat (răt)
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n.
1.
a. Any of various long-tailed rodents resembling mice but larger, especially one of the genus Rattus.
b. Any of various animals similar to one of these long-tailed rodents.
2. Slang
a. A despicable person, especially one who betrays or informs upon associates.
b. A scab laborer.
3. A pad of material, typically hair, worn as part of a woman's coiffure to puff out her own hair.
4. Slang A person who frequently passes time at a particular place. Often used in combination: a rink rat.
v. rat·ted, rat·ting, rats
v.intr.
1. To hunt for or catch rats, especially with the aid of dogs.
2. Slang To reveal incriminating or embarrassing information about someone, especially to a person in authority: ratted on his best friend to the police.
3. Slang To work as a scab laborer.
v.tr.
To puff out (the hair) with or as if with a pad of material.
Phrasal Verb:
rat out
Slang To reveal incriminating or embarrassing information about (someone), especially to a person in authority: ratted out the vandals to the school principal.

[Middle English, from Old English ræt; see rēd- in the Appendix of Indo-European roots.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. 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.

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