rat

noun
\ˈrat \

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

b : scab sense 3b

c : informer sense 2

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

rat

verb
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

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Other Words from rat

Noun

ratlike \ˈrat-ˌlīk \ 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.
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Recent Examples on the Web: Noun

Water percolates through such artificial embankments; the rats and land crabs soon destroy their integrity. Daniel C. Schlenoff, Scientific American, "“Foul Treachery” of Trotsky and Lenin in 1918; Phineas Gage’s Brain in 1868," 13 July 2018 The home was infested with cockroaches, mice, rats and bedbugs, and had a strong odor of feces, according to the release, which did not provide the location of the residence. Jesse Garza, Milwaukee Journal Sentinel, "Children left alone removed from vermin-infested Milwaukee home," 12 Mar. 2018 Since Dora came back, Christo has been bringing her dead rats to eat and giving her sticks to help renovate her nest. Shannon Barbour, Cosmopolitan, "This New York Hawk Love Triangle Proves Love Is Dead," 6 Mar. 2018 Moreover, the next generation of rats emulated their own mothers’ behavior: High-licking moms begat high-licking children. Judith Newman, New York Times, "Adversity Needn’t Thwart or Define You. Here’s How to Cope.," 6 July 2018 As the dam gates opened, a small band of river rats caught a once-in-a-lifetime ride. The Editors, Outside Online, "The Best Travel Stories We've Ever Told," 1 July 2018 Caloric restriction can increase the median life span of rats by 14 to 45 percent, reducing inflammation, oxidative stress, cholesterol, triglycerides, and the risk of tumors and cardiovascular disease, and improving the immune system. Jacqueline Detwiler, Popular Mechanics, "I Hacked My Body So You Don't Have To," 25 June 2018 The majority of rats vastly preferred the faux sugar over the alcohol option. Bret Stetka, Scientific American, "Scientists Pinpoint Brain Region That May Be Center of Alcohol Addiction," 21 June 2018 The Eternal Jew, an anti-Semitic propaganda film released in 1940, compares a map of Jewish migration to a pulsating pile of rats; Jews weren’t just considered animals, but plague-bearing animals at that. Sarah Jones, The New Republic, "Why Tyrants Dehumanize the Powerless," 20 June 2018

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.

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First Known Use of rat

Noun

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

Verb

1812, in the meaning defined at intransitive sense 1

History and Etymology for rat

Noun

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.

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Learn More about rat

Dictionary Entries near rat

raster

rastik

rasure

rat

rat's ass

rat's-tail fescue

rata

Statistics for rat

Last Updated

8 Oct 2018

Look-up Popularity

Time Traveler for rat

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

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More Definitions for rat

rat

noun

English Language Learners Definition of rat

 (Entry 1 of 2)

: a small animal that has a pointed nose and a long, thin tail

: a person who is not loyal or who cannot be trusted

: a person who is bad or cruel

rat

verb

English Language Learners Definition of rat (Entry 2 of 2)

: to tell someone in authority (such as the police) about something wrong that someone has done : to betray someone ( US )

rat

noun
\ˈrat \

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

rat

verb
ratted; ratting

Kids Definition of rat (Entry 2 of 2)

: to betray a friend

rat

noun
\ˈrat \

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)

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