What does rat mean?
A rat is a medium-sized, long-tailed rodent, especially the brown rat or black rat, and it is one of the most familiar wild animals in towns and cities worldwide. Rats are highly adaptable, living in drains, warehouses, gardens, and homes wherever food and shelter are available. The word can also refer to an informant who betrays someone to the authorities, and as a verb it means to provide information about another person. This second meaning is informal and usually carries a negative or disapproving connotation. In everyday use, rat often suggests a troublesome animal associated with disease, damage, and filth, even when those associations are not literally present. The word is useful because it bridges a literal animal familiar to many people and a figurative description of someone who discloses information or causes trouble.
A long-tailed rodent of the genus Rattus, especially the brown rat or black rat.
"The restaurant called an exterminator after finding a rat in the storeroom."
The term is neutral when identifying the species, though it commonly carries unpleasant associations in urban and domestic contexts.
An informant who betrays or gives information about someone else.
"She accused the rat of revealing the plan to the authorities."
This sense is informal and generally negative or derogatory.
To inform on someone or disclose information about another person.
"Several gang members began to rat on one another after the arrests."
Informal and usually disapproving; it can suggest betrayal or disloyalty.
The standard plural is 'rats'.
"The rats were nesting beneath the old shed."
A rat can survive in nearly any environment that provides food and shelter, which is why it has become one of humanity's most successful fellow travelers.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does rat come from?
The English word comes from Old English 'rata', an attested Germanic form referring to the animal; the deeper prehistoric origin is uncertain. The related verb meaning 'to inform' developed from the animal's supposed habit of deserting or consuming fellow creatures and came to mean, by extension, to betray or inform on someone. The word entered common Middle English usage in both its animal and informant senses.
Related word forms
How rat is actually used
The noun is standard in British and American English. The verb meaning 'to inform on someone' is informal and often derogatory or disapproving, particularly in British usage; in American English it is also used but may sound especially informal or accusatory.
Easily confused with rat
A mouse is generally smaller and has proportionally larger ears, while a rat is typically larger, heavier-bodied, and commonly associated with urban or underground environments.