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

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

When John Robinson remarried in late 2022, his guests at the Duquesne Club in downtown Pittsburgh were greeted with an inflatable rat.

From The Wall Street Journal • Apr. 5, 2026

A famous mine-clearing rat, who was awarded a gold medal for his heroism, has been commemorated with the world's first statue dedicated to a landmine-detecting rat.

From BBC • Apr. 4, 2026

Another Apopo-trained rat, named Ronin, set a new world record in 2025 by uncovering 109 landmines and 15 items of unexploded ordnance since 2021.

From BBC • Apr. 4, 2026

“Maybe what I need to do is just celebrate all I’ve done instead of getting back into this rat race, on this treadmill, and look for something totally different,” he said.

From Los Angeles Times • Mar. 6, 2026

Then I heard a mouse—a rat? —skitter off to my right.

From "Legendary Frybread Drive-In" by Cynthia Leitich Smith