rat

American  

[rat] / ræt /

noun

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

Conjugated Forms

Present

• has ratted
  perfect 3rd person singular
• have ratted
  perfect
• am ratting
  progressive 1st person singular
• is ratting
  progressive 3rd person singular
• have been ratting
  perfect progressive
• has been ratting
  perfect progressive 3rd person singular
• rats
  singular 3rd person
• are ratting
  progressive
• ratting
  participle

Past

• had ratted
  perfect
• was ratting
  progressive singular
• had been ratting
  perfect progressive
• were ratting
  progressive plural
• ratted
  participle
• ratted
  simple

Future

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

Rathbones Group RAT -4.25%decrease; red down pointing triangle was down 4.1%.

From The Wall Street Journal • Feb. 11, 2026

The RAT, a small propeller that extends from the underside of the Boeing 787 Dreamliner, acts as an emergency backup generator.

From BBC • Jul. 11, 2025

Lifeguards with the Los Angeles County Fire Department walked along RAT Beach, just south of Torrance Beach, warning people to stay out of the water, said Kealiinohopono Barnes, a spokesperson for the department.

From Los Angeles Times • Sep. 7, 2022

Due to the positive RAT, Ardern will be required to isolate until the morning of May 21, and undertake what duties she can remotely this week.

From Reuters • May 13, 2022

And he never stopped hearing those British battle drums, that ghostly RAT, tat, tat, tat, tat.

From I Survived the American Revolution, 1776 by Lauren Tarshis