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:
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
"We don't have robots that are nearly as good at understanding the physical world as a rat," says Yann LeCun, one of the leading figures in the world of artificial intelligence.
From BBC ● Jul. 2, 2026
The enclave has been struck with a severe rat infestation fueled by uncollected trash and warmer weather.
From The Wall Street Journal ● May 24, 2026
The Andes virus, which circulates in Argentina and Chile and is mainly spread among the long-tailed pygmy rice rat, is the only hantavirus strain known to be able to transmit from human to human.
From Los Angeles Times ● May 14, 2026
The rat interrupted these painful questions with another: “Where’d your funny human eyeglass go, fox? You look horrible.”
From "The Undead Fox of Deadwood Forest" by Aubrey Hartman
The team next used fiber photometry to monitor orexin neuron activity in real time while the rats waited for and received food.
From Science Daily ● Aug. 5, 2026
Although the stimulation successfully activated the cells, it did not cause the rats to work harder or show any further rise in motivation.
From Science Daily ● Aug. 5, 2026
“We are still concerned about whether or not there is enough staffing to keep up with pest control,” the rats and flies, Rodarte said.
From Los Angeles Times ● Jul. 30, 2026
I spent most of my adult life near downtown Brooklyn, where my encounters with wildlife were limited to pigeons and rats.
From The Wall Street Journal ● Jul. 26, 2026
Here he was fighting off a dozen rats, trying to rescue the Vole family, while Basil was dusting out his den!
From "Redwall" by Brian Jacques
No one would get ratted out on social media as “problematic.”
From The Wall Street Journal ● Feb. 21, 2026
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
Among the $1 items found at the weekly Sunday sale at Jet Rag, I encountered the remains of ratted paraphernalia and uniforms distinct to the American ideology of waste.
From Los Angeles Times ● Dec. 1, 2021
Her hair ratted, her nose smudged, and she left handprints wherever she went.
From "The Girl Who Drank the Moon" by Kelly Barnhill
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
Stroup has said that ratting out Peter Bourne was the “stupidest decision” he ever made.
From Slate ● Dec. 23, 2025
"But he could be ratting out Eastman and Powell, for example, in order to make a deal."
From Salon ● Jun. 29, 2023
He prided himself on not ratting out his Watergate co-conspirators and argued that if everyone had just shut up about it Nixon would not have been deposed.
From Washington Post ● Mar. 31, 2021
First, the regular student code about not ratting people out—that didn’t apply at the Academy.
From "Ungifted" by Gordon Korman
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.
