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
Gina Lee Castro, Journal Sentinel, 20 Nov. 2024
Capsaicin can be lethal to rats and mice, and symptoms of acute oral toxicity can include a staggering gait, skin redness, and cyanosis — blue lips, nail beds, and skin due to low oxygen levels.
—Amiah Taylor, Discover Magazine, 13 Nov. 2024
This could become another rat’s nest of lawsuits and counter lawsuits.
—Andrew J. Hawkins, The Verge, 6 Nov. 2024
But the trainable rats have an acute sense of smell.
—Ashley Strickland, CNN, 2 Nov. 2024
See all Example Sentences for rat 
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Noun
In September, Bay View residents questioned whether raccoons and other wildlife were being affected by rat poison.
—Gina Lee Castro, Journal Sentinel, 20 Nov. 2024
Capsaicin can be lethal to rats and mice, and symptoms of acute oral toxicity can include a staggering gait, skin redness, and cyanosis — blue lips, nail beds, and skin due to low oxygen levels.
—Amiah Taylor, Discover Magazine, 13 Nov. 2024
This could become another rat’s nest of lawsuits and counter lawsuits.
—Andrew J. Hawkins, The Verge, 6 Nov. 2024
But the trainable rats have an acute sense of smell.
—Ashley Strickland, CNN, 2 Nov. 2024
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 26 Nov. 2024.
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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