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

see also:

smell a rat

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 of rat

Noun

• informant
• informer
• canary
• reporter

Verb

• split (on)
• talk
• grass (on)
• 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

When a sensor detected movement in a rat’s front paw, another device was automatically activated to stimulate a hind-leg muscle, producing a contraction that mimicked part of the animal’s natural walking motion. — Neetika Walter, Interesting Engineering, 25 Sep. 2026

In the county, health officials said infected fleas often are found on rats, free-roaming cats and opossums. — Ruben Vives, Los Angeles Times, 24 Sep. 2026

There are cities where rats are glimpsed at night, furtively scurrying into a dark corner or among the train tracks. — David A. Graham, The Atlantic, 18 Sep. 2026

Alas, poor Bryan is about to learn the hard way that change — as the saying goes — is as hard to outrun as an ever-growing zombie rat king with 37 different limbs and a weirdly personal vendetta. — David Ehrlich, IndieWire, 16 Sep. 2026

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

1810, in the meaning defined at intransitive sense 1

Phrases Containing rat

• black rat snake
• brown rat
• eastern rat snake
• gray rat snake
• hood rat
• 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)