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:
The intrigue is thick; Johnny is a rat; “War” might have been called “The Lawyer Who Came in From the Cold.”
From The Wall Street Journal ● Sep. 29, 2026
The most famous are "lying flat", when people opt out of the rat race entirely, and "involution", a rather clunky term now commonly used to describe intense competition which generates little meaningful reward.
From BBC ● Sep. 26, 2026
In its 2026 review, the European Food Safety Authority noted that the compounds detected in the rat study could have been impurities already present in the administered sucralose.
From Science Daily ● Sep. 14, 2026
"Our younger generation... they're always in this little rat race, keeping up with social media," the 61-year-old said.
From Barron's ● Sep. 7, 2026
“Hank, don’t freak out,” she says, “but I think there’s a rat in here. See that squash moving across the floor?”
From "Invisible Inkling" by Emily Jenkins
Rats that had received both medications regained less weight than rats treated only with tirzepatide.
From Science Daily ● Oct. 11, 2026
Gym rats can check their body composition of fat and muscle, people with heart issues can get their heartbeat captured, and mole owners can get their moles mapped to 0.1 mm.
From Slate ● Oct. 8, 2026
It added that the food incident was isolated and re-labelling unsold food was not company policy, but it did not comment on the rats claim.
From BBC ● Sep. 29, 2026
Warming oceans, habitat destruction, predation by rats and dogs, competition with commercial fisheries and accidental capture in fishing nets are also threatening many populations.
From Science Daily ● Sep. 22, 2026
“The rats are deserting the ship. We must be sinking!”
From "Secrets at Sea" by Richard Peck
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
The heavy black eyeliner and white-face makeup, the holey fishnets and ratted hair — these also serve as a beacon to fellow misfits, a way of finding your tribe while scaring off the normals.
From Los Angeles Times ● May 22, 2023
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
Bulger, who ran the largely Irish mob in Boston in the 1970s and ’80s, served as an FBI informant who ratted on his gang’s main rival, according to the bureau.
From Seattle Times ● Aug. 23, 2022
When someone ratted on him, the police questioned Cole.
From "Touching Spirit Bear" by Ben Mikaelsen
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
"But he could be ratting out Eastman and Powell, for example, in order to make a deal."
From Salon ● Jun. 29, 2023
Which is, you know, the problem here, and what all who tuned in should now be ratting him out for.
From Washington Post ● Oct. 21, 2019
With the Cambridge Analytica scandal still ratting along, Facebook revealed that a separate problem had exposed almost 50 million accounts to being hijacked.
From BBC ● Dec. 29, 2018
Dad’s going to drag me to school, and my name will be mud for ratting them out.
From "Shooting Kabul" by N. H. Senzai
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Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
