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

Other Words from rat Synonyms More Example Sentences Learn More about rat

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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

Not everyone is completely convinced that the rats were really into hide and seek. — Jason Daley, Smithsonian, "Rats Learned to Play Hide and Seek to Help Study the Brain," 13 Sep. 2019 Dear Readers: Got a varmint problem? Poisoning rats and mice is bad for many reasons. — Washington Post, "Hints From Heloise: Turtle time!," 31 Aug. 2019 But not everyone agrees that a rat is the best pet for their class, including her best friend, Maya. — Ciarra Chavarria, NBC News, "10 awesome books for young girls that encourage and celebrate STEM," 29 Aug. 2019 Interest has also been high in developing gene drives to rein in rats and mice, which as invasive species often acutely threaten wildlife. — Quanta Magazine, "Gene Drives Work in Mice (if They’re Female)," 27 Aug. 2019 Du Bey said the loss of permits would have devastated the production company, and a union protest with a large, inflatable rat would have been similarly disruptive. — Milton J. Valencia, BostonGlobe.com, "Walsh aide testifies pressuring Boston Calling to use union workers was unfair," 1 Aug. 2019 The bill would impact species covered by the Animal Welfare Act, which regulates the treatment of warm-blooded animals except for mice, rats and birds. — Tara Law, Time, "Senate Bill Could Save Many Federal Lab Animals' Lives and Give Them a New Home," 30 July 2019 Scientist Hiromitsu Nakauchi wants to create a human pancreas in rodents like rats and mice, and the Japanese government, specifically its education and science ministry, has issued new guidelines that open up the procedures to anyone. — David Grossman, Popular Mechanics, "I Guess You Can Grow a Human Pancreas In a Rat Now," 26 July 2019 Great horned owls, also known as tiger owls, typically feed on rabbits and hares, rats and mice, or other rodents. — Fox News, "Great horned owl discovered completely covered in oil after getting into pit," 23 July 2019

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.

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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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)

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

See the full definition for rat in the English Language Learners Dictionary

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)