\ ˈrat How to pronounce rat (audio) \

Definition of rat

 (Entry 1 of 2)

1a : 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
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

Definition of rat (Entry 2 of 2)

intransitive verb

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

transitive verb

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

Other Words from rat


ratlike \ ˈrat-​ˌlīk How to pronounce rat (audio) \ adjective

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: Noun Remy is a rat with humanoid characteristics living in Paris with a talent for cooking. Nitya Rao, Seventeen, 20 July 2022 One lieutenant found a toy rat in his office mailbox; another lieutenant, who was cooperating with a grand jury investigation into the department, accused Cachopa of attempting to strike him with his SUV in the parking lot of Town Hall. Laura Crimaldi, BostonGlobe.com, 20 June 2022 Bratsenis built a notorious criminal resume in the 1970s and ‘80s, after graduating from Stamford High School in 1966 and fighting as a tunnel rat in Vietnam while serving in the U.S. Marine Corp. from 1968 to 1972. courant.com, 5 Apr. 2022 In The City Rat and the Country Rat, a rat in Paris invites his rural friend for a taste of the high life, courtesy of the master of the house’s larder. Brian T. Allen, National Review, 10 Mar. 2022 Another problem fraying the bolt: There’s a rat in their midst, passing tapes of their conversations to their enemies. Leslie Felperin, The Hollywood Reporter, 14 Feb. 2022 Podmore grew up a river rat in Colorado, with his parents taking the family down desert waterways at every opportunity, and his love for these silty rivers is clear throughout this essay collection. The Editors, Outside Online, 22 Apr. 2020 Rodenticide, more commonly known as rat poison, can cause second-generation anticoagulant rodenticide, or SGAR, poisoning. Anjali Huynh, BostonGlobe.com, 16 June 2022 Hickey goes on to read Gober’s stacks of newspapers and boxes of rat poison placed within a paint-by-numbers wraparound wallpaper of a New England forest as situated between the history of American transcendentalism and the raging AIDS crisis. Jarrett Earnest, The New York Review of Books, 8 June 2022 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'rat.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of rat


before the 12th century, in the meaning defined at sense 1a


1812, in the meaning defined at intransitive sense 1

History and Etymology for rat


Middle English rat, ratte, going back to Old English ræt (attested once), akin to Old Saxon ratta "rat," Middle Dutch ratte, rotte, Old High German ratta, radda, ratza (feminine weak nouns), also Old High German rato (masculine weak noun), probably going back to an ablauting paradigm *raþō (nominative), *rattaz/*ruttaz (genitive), *radeni/*rudeni (dative), going back to earlier *(H)rót-ōn, *(H)rt-n-ós, *(H)rt-én-i, of uncertain origin

Note: The origin of the etymon beyond Germanic is obscure. Regionally in German Ratz or Ratze are applied to other animals (as the dormouse and the polecat); if these senses are old, the application of the etymon to rats (Rattus rattus, Rattus norvegicus) may be secondary. Note that if the base is pre-Germanic *rat-, there is no connection to either Latin rōdere "gnaw, nibble, eat away" (see rodent) or rādere "scrape, shave" (see rase), as has often been assumed.

Learn More About rat

Time Traveler for rat

Time Traveler

The first known use of rat was before the 12th century

See more words from the same century

Dictionary Entries Near rat



rat's ass

See More Nearby Entries 

Statistics for rat

Last Updated

5 Aug 2022

Cite this Entry

“Rat.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rat. Accessed 9 Aug. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for rat


\ ˈrat How to pronounce rat (audio) \

Kids Definition of rat

 (Entry 1 of 2)

1 : a gnawing animal with brown, black, white, or grayish fur that looks like but is larger than a mouse
2 : a person who betrays friends


ratted; ratting

Kids Definition of rat (Entry 2 of 2)

: to betray a friend


\ ˈrat How to pronounce rat (audio) \

Medical Definition of rat

: 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)

More from Merriam-Webster on rat

Nglish: Translation of rat for Spanish Speakers

Britannica English: Translation of rat for Arabic Speakers

Britannica.com: Encyclopedia article about rat


Test Your Vocabulary

Odd Habits and Quirks

  • image1926873504
  • Which of the following best describes an easily irritated person?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!