rat

1 of 2

noun

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
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
ratlike adjective

rat

2 of 2

verb

ratted; ratting

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

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
Further study of rat heart cells suggests the new compounds do more strongly mimic the effects of exercise. Lindsey Leake, Fortune Well, 18 Mar. 2024 That chain was recently fined more than $40 million for a rat infestation at a warehouse, forcing hundreds of stores to close temporarily. Chris Morris, Fortune, 15 Mar. 2024 This story of the sweet camaraderie between a naive pig and his wise spider friend — with lovable supporting characters like Ram, Goose, and Templeton the gluttonous rat — still spins quite the spellbinding web after all these years. Ew Staff, EW.com, 14 Mar. 2024 At Sundance, comfort was key given the adverse weather, but that was also where Stewart leaned into gym rat territory, rocking a white muscle tank with red and white striped track pants, and Adidas Superstars. Hannah Jackson, Vogue, 14 Mar. 2024 Joining the rats, the building is also home to a cockroach infestation, mold, no air conditioning, and elevators and bathrooms that don't function properly, the superintendent added. Emma Colton, Fox News, 13 Mar. 2024 Julie Menin, a councilwoman on Manhattan’s East Side, has been trying to smoke rats out of her district by having an exterminator pump carbon monoxide into their holes. Jane Margolies, New York Times, 13 Mar. 2024 Spread by black rats, this plague is the same culprit behind the infamous Black Death that rocked Medieval Europe between 1347 to 1351, killing millions of people. Sean Mowbray, Discover Magazine, 7 Mar. 2024 Last year’s report cards famously revealed that the Jacksonville Jaguars had a temporary rat infestation in the locker room, though the team scored highly this year having opened a shiny new training facility in June. George Ramsay, CNN, 29 Feb. 2024

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'rat.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Etymology

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.

First Known Use

Noun

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

Verb

1812, in the meaning defined at intransitive sense 1

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

Dictionary Entries Near rat

Cite this Entry

“Rat.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rat. Accessed 29 Mar. 2024.

Kids Definition

rat

1 of 2 noun
1
: 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
ratlike adjective

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)

More from Merriam-Webster on rat

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