View synonyms for rat


[ rat ]


  1. any of several long-tailed rodents of the family Muridae, of the genus Rattus and related genera, distinguished from the mouse by being larger.
  2. any of various mammals similar to or related to the long-tailed rodents of the genus Rattus.
  3. Slang. a scoundrel.
  4. Slang.
    1. a person who abandons or betrays their party or associates, especially in a time of trouble.
    2. a scab laborer.
  5. Slang. a person who frequents a specified place: gym rats.

    a mall rat;

    gym rats.

  6. a pad with tapered ends formerly used in women's hairstyles to give the appearance of greater thickness.


  1. rats, Slang. (an exclamation of disappointment, disgust, or disbelief.)

verb (used without object)

, rat·ted, rat·ting.
  1. Slang.
    1. to desert one's party or associates, especially in a time of trouble.
    2. to turn informer; squeal:

      He ratted on the gang, and the police arrested them.

    3. to work as a scab.
  2. to hunt or catch rats.

verb (used with object)

, rat·ted, rat·ting.
  1. to make (the hair) appear thicker by use of a small pad of material or by teasing.

verb phrase

  1. Slang. to inform on:

    He ratted out his partners in exchange for a lighter sentence.


/ ræt /


  1. any of numerous long-tailed murine rodents, esp of the genus Rattus , that are similar to but larger than mice and are now distributed all over the world See also brown rat black rat
  2. informal.
    a person who deserts his or her friends or associates, esp in time of trouble
  3. informal.
    a worker who works during a strike; blackleg; scab
  4. slang.
    an informer; stool pigeon
  5. informal.
    a despicable person
  6. smell a rat
    to detect something suspicious


  1. informal.
    intrusually foll byon
    1. to divulge secret information (about); betray the trust (of)
    2. to default (on); abandon

      he ratted on the project at the last minute

  2. to hunt and kill rats

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Derived Forms

  • ˈratˌlike, adjective

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Other Words From

  • rat·like adjective

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Word History and Origins

Origin of rat1

First recorded before 1000; Middle English rat(t)te, Old English ræt; cognate with Dutch rat, German Ratz, Ratte

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Word History and Origins

Origin of rat1

Old English rætt ; related to Old Saxon ratta , Old High German rato

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Idioms and Phrases

  1. smell a rat, to suspect or surmise treachery; have suspicion:

    After noting several discrepancies in his client's story, the attorney began to smell a rat.

More idioms and phrases containing rat

  • like a drowned rat
  • smell a rat

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Example Sentences

Both groups produced similar hormone spikes when stressed, but in the juvenile rats, levels took much longer to return to normal.

The team has already been placing them in rats and primates.

From Fortune

Other researchers studied what happens when adolescent rats move into “enriched” environments.

Blueberry-fed rats spent almost 70 percent of their time exploring the new object, as expected of animals that recognized the old object.

Even if they find your trash can instead, he adds, “that’s necessarily going to support fewer rats.”

One rat had once fallen on his head, he said, during a rat raid of a local home.

Since rat root comes from a plant that grows on the edge of the lake there are concerns that the plant is carrying toxins.

Chief Adam offers us some of the local medicine called rat root.

The episode includes satirical images of crime-ridden, rat-infested slums overrun by child-biting monkeys.

A cabin filled with the Rat Pack and the ladies who loved them.

Next morning Judy shouted that there was a rat in the nursery, and thus he forgot to tell her the wonderful news.

He had repeated till he was thrice weary the statement that "the Cat lay on the Mat and the Rat came in."

Growling horribly, the enraged brute seized poor Pearson and shook him as a terrier dog shakes a rat.

I was here a little while ago and nobody answered my knock, though I could hear that typewriter going rat, tat, tat all the time.

Rat this pawn of the Eye may have been, but even a cornered rat will fight with the courage of a lion.


Definitions and idiom definitions from Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.