rat

American  

[rat] / ræt /

noun

rats plural

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. an informer.

   3. 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.

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interjection

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

verb (used without object)

rats, present (3rd person singular) ratted, past participle, past ratting present participle

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)

rats, present (3rd person singular) ratted, past participle, past ratting present participle

1. to make (the hair) appear thicker by use of a small pad of material or by teasing.

verb phrase

1. rat out to inform on.

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

idioms

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.

rat British  

/ ræt /

noun

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. to detect something suspicious

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verb

1. informal

   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

rat More Idioms  

More idioms and phrases containing rat

• like a drowned rat
• smell a rat

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Other Word Forms

Derived Forms

• ratlike
  adjective

Inflected Forms

Nouns

• rats
  plural

Participles

• ratting
  present
• ratted
  past

Conjugated Forms

Present

• rat
  simple
• rats
  simple
• have ratted
  perfect
• has ratted
  perfect
• am ratting
  progressive
• are ratting
  progressive
• is ratting
  progressive
• have been ratting
  perfect progressive
• has been ratting
  perfect progressive

Past

• ratted
  simple
• had ratted
  perfect
• was ratting
  progressive
• were ratting
  progressive
• had been ratting
  perfect progressive

Future

• will rat
  simple
• will have ratted
  perfect
• will be ratting
  progressive
• will have been ratting
  perfect progressive

Etymology

Origin of rat

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

Explanation

Rats are mouse-like rodents with long tails, pointed noses, and whiskers. Rats are often associated with filth and disease. So, if someone calls you a rat, it's not like being called a fox. It's an insult. Many people keep rats as pets, and scientists often study rats because their psychological behavior is actually very similar to that of humans. Rats are intelligent and adaptable, but wild rats also carry disease and sometimes bite humans. These negative traits have led to the informal meaning of rat, "hateful person," "liar," or "double-crosser." You can also use rat as a verb to mean "betray or snitch on."

Example Sentences

The Horse enemies are the Rat and the Ox.

From Los Angeles Times • Feb. 10, 2026

Her performance as the Rat Queen in "The Nutcracker" for almost a month drew praise for its sophistication.

From Barron's • Jan. 30, 2026

Rat concerns in Mid Ulster come a week after some residents in Strabane described an ongoing rodent problem in their properties as "absolute hell".

From BBC • Jan. 20, 2026

Los Angeles and Las Vegas steakhouses, he believes, lean into the Rat Pack era of red leather booths and massive shrimp cocktails.

From Los Angeles Times • Oct. 31, 2025

Rat Kiley had lost his best friend in the world.

From "The Things They Carried" by Tim O'Brien