1
a
: any of numerous rodents (Rattus and related genera) differing from the related mice especially by considerably larger size
b
: any of various similar rodents
2
: a contemptible person: such as
a
: one who betrays or deserts friends or associates
b
c
3
: a pad over which a woman's hair is arranged
4
: a person who spends much time in a specified place
a mall rat
ratted; ratting
1
: to betray, desert, or inform on one's associates
—usually used with on
2
: to catch or hunt rats
3
: to work as a scab
1
: to give (hair) the effect of greater quantity (as by use of a rat)
2
: to inform on : turn in
—usually used with out
ratted out his accomplice
Synonyms of rat
Relevance
Noun
Verb
Examples of rat in a Sentence
Noun
a dirty old building infested by rats and mice
I can't believe that rat turned us in to the police!
No one understands why she's with a rat like him.
Every night he goes to work out with the other gym rats.
Verb
The teacher knows what we did, which means that somebody ratted.
Recent Examples on the Web
Andrew Paul, Popular Science, 27 Nov. 2025
Born out of Sydney in 1999 by a group of friends fed up with cookie-cutter jeans, Ksubi staked its name on provocation with an ethos forged in defiance; its 2001 debut infamously included 200 live rats on the runway.
—Alexandra Harrell, Sourcing Journal, 25 Nov. 2025
The hundreds of rats and mice were sick and had to be treated twice a day with vaporized medicine.
—Kelly Puente, Nashville Tennessean, 25 Nov. 2025
The discomfort that arises in watching Perfidia rat on her comrades or Lockjaw proclaim his rapacious desire for Black girls courses through the finale.
—Angelica Jade Bastién, Vulture, 24 Nov. 2025
See All Example Sentences for rat
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Noun
There are also multiple recipes jotted down for rat poisons–likely a necessity at Darwin’s small estate in Down, England, that included outbuildings and stables.
—Andrew Paul, Popular Science, 27 Nov. 2025
Born out of Sydney in 1999 by a group of friends fed up with cookie-cutter jeans, Ksubi staked its name on provocation with an ethos forged in defiance; its 2001 debut infamously included 200 live rats on the runway.
—Alexandra Harrell, Sourcing Journal, 25 Nov. 2025
The hundreds of rats and mice were sick and had to be treated twice a day with vaporized medicine.
—Kelly Puente, Nashville Tennessean, 25 Nov. 2025
The discomfort that arises in watching Perfidia rat on her comrades or Lockjaw proclaim his rapacious desire for Black girls courses through the finale.
—Angelica Jade Bastién, Vulture, 24 Nov. 2025
See All Example Sentences for rat
Cite this Entry
“Rat.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rat. Accessed 29 Nov. 2025.
Copy CitationKids Definition
rat
1 of 2 noun1
: any of various rodents that have brown, black, white, or grayish fur and a long usually nearly hairless tail and that look like but are larger than the related mice
2
: a person who betrays friends
3
: a person who spends much time in a specified place
a mall rat
rat
2 of 2 verb
ratted; ratting
1
: to betray, desert, or inform on one's friends
didn't rat on us
ratted them out
2
: to catch or hunt rats
Medical Definition
rat
noun
: any of the numerous rodents (family Muridae) of Rattus and related genera that differ from the murid mice by their usually considerably larger size and by features of the teeth and other structures and that include forms (as the brown rat, the black rat, and the roof rat) which live in and about human habitations and in ships, have become naturalized by commerce in most parts of the world, and are destructive pests consuming or destroying vast quantities of food and other goods and acting as vectors of various diseases (as bubonic plague)
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