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
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
Omer Awan, Forbes.com, 13 July 2025
Fulton County was reported to have 318 rodents for every 1,000 homes, while Susquehanna County was found to have 301 mice and rats per 1,000 housing units.
—Soo Kim, MSNBC Newsweek, 9 July 2025
Separated by accident from his colony, Remy ends up hiding out at Gusteau’s old restaurant, now owned by the tyrannical, rat-hating chef Skinner.
—Pam Kragen, San Diego Union-Tribune, 8 July 2025
May 2025 – Controversial Match of the Day host Gary Lineker is forced to exit the BBC after sharing a video featuring a cartoon rat – an antisemitic trope.
—Max Goldbart, Deadline, 4 July 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
The dye was linked to thyroid cancer risks in rats as well as behavioral issues in children such as hyperactivity.
—Omer Awan, Forbes.com, 13 July 2025
Fulton County was reported to have 318 rodents for every 1,000 homes, while Susquehanna County was found to have 301 mice and rats per 1,000 housing units.
—Soo Kim, MSNBC Newsweek, 9 July 2025
Separated by accident from his colony, Remy ends up hiding out at Gusteau’s old restaurant, now owned by the tyrannical, rat-hating chef Skinner.
—Pam Kragen, San Diego Union-Tribune, 8 July 2025
May 2025 – Controversial Match of the Day host Gary Lineker is forced to exit the BBC after sharing a video featuring a cartoon rat – an antisemitic trope.
—Max Goldbart, Deadline, 4 July 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 25 Jul. 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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