rat

1 of 2

noun

ˈrat 

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

: 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

ratlike

ˈrat-ˌlīk 

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

Synonyms

Noun

• informant
• informer
• canary [slang]
• reporter

Verb

• split (on) [British]
• talk
• grass (on) [British slang]
• tell (on)
• inform

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

What This Means For You Recent research linking glyphosate, a common weedkiller ingredient, to cancer in rats raises new concerns about its safety for humans. —Fran Kritz, Verywell Health, 20 June 2025

In the delightful Ratatouille, Remy the rat (Patton Oswalt) struggles to fit in. —Meg Walters, EW.com, 19 June 2025

Players mockingly shoot plastic rats at the King Rat after wins. —Dave Hyde, Sun Sentinel, 16 June 2025

Residents say the streets look neater and rat sightings are down. —Arkansas Online, 15 June 2025

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

Phrases Containing rat

• black rat snake
• brown rat
• eastern rat snake
• gray rat snake
• kangaroo rat
• lab/laboratory rat
• like a drowned rat
• mole rat
• naked mole rat
• Norway rat
• pack rat
• rat-arsed
• rat-a-tat
• rat-a-tat-tat
• rat-bite fever
• rat cheese
• rat fink
• rat race
• rat run
• rat snake
• rat-tail file
• rat trap cheese
• red rat snake
• rug rat
• smell a rat
• the rat race
• water rat
• western rat snake
• wood rat

Rhymes for rat

• at
• bat
• batt
• brat
• cat
• chat
• fat
• flat
• gat
• gnat
• hat
• kat

Kids Definition

rat

1 of 2 noun

ˈrat 

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

-ˌlīk 

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

ˈrat 

: 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)