rat
Americannoun
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rats
plural
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any of several long-tailed rodents of the family Muridae, of the genus Rattus and related genera, distinguished from the mouse by being larger.
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any of various mammals similar to or related to the long-tailed rodents of the genus Rattus.
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Slang. a scoundrel.
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Slang.
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a person who abandons or betrays their party or associates, especially in a time of trouble.
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an informer.
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a scab laborer.
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Slang. a person who frequents a specified place: gym rats.
a mall rat;
gym rats.
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a pad with tapered ends formerly used in women's hairstyles to give the appearance of greater thickness.
interjection
verb (used without object)
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rats,
present (3rd person singular)
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ratted,
past participle, past
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ratting
present participle
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Slang.
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to desert one's party or associates, especially in a time of trouble.
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to turn informer; squeal.
He ratted on the gang, and the police arrested them.
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to work as a scab.
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to hunt or catch rats.
verb (used with object)
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rats,
present (3rd person singular)
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ratted,
past participle, past
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ratting
present participle
verb phrase
idioms
noun
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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
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informal a person who deserts his or her friends or associates, esp in time of trouble
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informal a worker who works during a strike; blackleg; scab
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slang an informer; stool pigeon
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informal a despicable person
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to detect something suspicious
verb
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informal
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to divulge secret information (about); betray the trust (of)
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to default (on); abandon
he ratted on the project at the last minute
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to hunt and kill rats
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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ratsimple
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ratssimple
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have rattedperfect
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has rattedperfect
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am rattingprogressive
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are rattingprogressive
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is rattingprogressive
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have been rattingperfect progressive
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has been rattingperfect progressive
Past
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rattedsimple
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had rattedperfect
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was rattingprogressive
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were rattingprogressive
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had been rattingperfect progressive
Future
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
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
“Josh,” a gym rat and “protein maximizer,” said a bar needed more than 15 grams of protein to make it into his daily “stack.”
From The Wall Street Journal ● Aug. 19, 2026
His deceit was uncovered when Helen's son smelt a rat and applied for Clare's Law, external, where you can ask if someone has a history of abusive offending.
From BBC ● Jul. 15, 2026
They used the rat tapeworm Hymenolepis diminuta, a non-pathogenic species commonly used to study interactions among parasites, gut microorganisms, and the immune system because of its known anti-inflammatory properties.
From Science Daily ● Jul. 10, 2026
In California, the cats’ population faces several threats — including human encroachment, loss of habitat and prey due to wildfires, rat poison, disease and vehicle collisions.
From Los Angeles Times ● Jun. 6, 2026
The clatter of the falling cans sends the rat squealing and sets Mav barking from inside the house.
From "Red Flags and Butterflies" by Sheryl Azzam
Like rats in a Skinner box being conditioned to get food or stop pain, AI models hill-climb in a process similar to reinforcement learning, tweaking their parameters based on feedback.
From The Wall Street Journal ● Aug. 14, 2026
Noxious smoke and an influx of rats and flies attracted to rotting meat stored at the facility have tormented neighbors.
From Los Angeles Times ● Aug. 12, 2026
Several people, including former rebel fighter Motaz al-Zaydi, told us they had resorted to eating rats.
From BBC ● Aug. 7, 2026
They then placed the rats in a progressive ratio test, in which the animals had to make an increasing number of touches to receive each food reward.
From Science Daily ● Aug. 5, 2026
Cocoa barks at a couple of rats that run around.
From "The Manifestor Prophecy" by Angie Thomas
As a young woman in the 1920s, she disguised herself as a man and worked on a local archaeological dig at the Roman Villa Casale until she was ratted out and sent packing.
From The Wall Street Journal ● Aug. 21, 2026
“She ratted me out! Yes, I have the teapot, which I realize is quite the memento,” says Krasinski, writing while in production on an upcoming project.
From Los Angeles Times ● Mar. 24, 2025
Finally, Perry himself turns on his schoolteacher girlfriend, Ginny Aimes, on a dime when the gun is brought to light, assuming she is the person who ratted him out.
From New York Times ● Apr. 10, 2023
Simone now knew she had ratted him out.
From Seattle Times ● Oct. 16, 2022
The ratted fur of its neck mopped the ground.
From "The Many Assassinations of Samir, the Seller of Dreams" by Daniel Nayeri
And who wouldn’t have to modify their behavior if they thought Rover was ratting them out to his pals down at Paws & Claws?
From The Wall Street Journal ● Feb. 3, 2026
"I don't know how I feel about the culture of ratting out your neighbours," Ms Morfopoulos said.
From BBC ● Sep. 6, 2023
"But he could be ratting out Eastman and Powell, for example, in order to make a deal."
From Salon ● Jun. 29, 2023
This particular Planned Parenthood is where high school girls in my town would go if they needed birth control and didn’t want any busybodies ratting them out if they were spotted at the local clinic.
From Washington Post ● Jan. 27, 2023
Also I think he hopes I will do some ratting on Monsieur Laurel and Mademoiselle Hardy.
From "Code Name Verity" by Elizabeth Wein
Definitions and idiom definitions from Dictionary.com 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.
