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
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
Brian Davids, The Hollywood Reporter, 21 Feb. 2025
Four black rats were confirmed to have H5N1 avian flu in late January in Riverside County, California, where two recent poultry outbreaks were reported, the agency said.
—Sara Moniuszko, CBS News, 20 Feb. 2025
Meanwhile, rats can have as many as 12 in one litter, while rabbits can have as many as 14.
—Josh Hammer, Newsweek, 17 Feb. 2025
Gym rats push and pump weights to stay healthy and enjoy the side effect of looking buff in the process.
—David Oliver, USA TODAY, 16 Feb. 2025
See all Example Sentences for rat 
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Noun
There’s something a bit slimy and a bit dirty about a kind of rat’s tail.
—Brian Davids, The Hollywood Reporter, 21 Feb. 2025
Four black rats were confirmed to have H5N1 avian flu in late January in Riverside County, California, where two recent poultry outbreaks were reported, the agency said.
—Sara Moniuszko, CBS News, 20 Feb. 2025
Meanwhile, rats can have as many as 12 in one litter, while rabbits can have as many as 14.
—Josh Hammer, Newsweek, 17 Feb. 2025
Gym rats push and pump weights to stay healthy and enjoy the side effect of looking buff in the process.
—David Oliver, USA TODAY, 16 Feb. 2025
See all Example Sentences for rat
Dictionary Entries Near rat
Cite this Entry
“Rat.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rat. Accessed 24 Feb. 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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