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)

ratted, ratting

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)

ratted, ratting

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

• ratlike adjective

Etymology

Origin of rat

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

Example Sentences

They were sued by several units in 2023 and 2024 over living conditions, including allegations of infestations of rats, vermin and cockroaches that tenants said made their lives “a living hell.”

From Los Angeles Times

They weren’t allowed to experiment with mammals, including rats, so they isolated tissue samples from anglerfish, the carnivorous bottom-feeders with razor sharp teeth.

From The Wall Street Journal

The genes of your roommate may be shaping the bacteria in your gut, and your genes may be influencing theirs, according to a rat study published on December 18 in Nature Communications.

From Science Daily

I’m not Joanna Stern, who wants singing cars and robot dishwashers and still elected to rat out the Journal’s AI vending machine for selling fine wine and delicious live fish.

From The Wall Street Journal

When everything from the rats to the Christmas tree get bigger, so does Clara as she goes from a young girl to an adolescent.

From Los Angeles Times