supergrass

1 9.9

A person who tells police the names of many criminals

noun
/ˈsuːpəɡrɑːs/

Archaic

: delator

Morris O Mahoney was a supergrass back in the day.

Examples

And they had Radiohead, they had Supergrass.

Coldplay: A Head Full of Dreams (2018)
Supergrass:

Chicago Cab (1998)
The police arrested the suspect after a supergrass revealed his involvement in the drug ring.
In the investigation, they relied heavily on a supergrass to gather evidence against the gang.
The trial was based on testimonies from a supergrass who identified several members of the organization.

Synonyms

grass

vssupergrass

Offensive

14 9.9

A person who tells the police about other people's crimes

is the same idea but stresses organized crime and wider groups

stoolie

vssupergrass

Offensive

3 9.9

A person who secretly gives information to the police, often from inside a group

provides wide evidence against many not only serving as a decoy

snitcher

vssupergrass

Offensive

1 8.7

A person who secretly tells the police about other people's crimes

focuses on giving evidence that implicates many people rather than private betrayals

stoolpigeon

vssupergrass

Slang

9.9

A person who secretly tells the police about criminals

is about implicating large networks rather than acting mainly as a decoy

copper's nark

vssupergrass

Slang

9.9

A person who secretly tells the police about crimes

focuses on implicating many people in organized crime rather than lone spying

Surface Forms

supergrass singular

supergrasses plural

Morphology

supergrass = grass (semi-transparent) = super + grass

Formally 'super' + 'grass' and the meaning 'especially important informer' is predictable if the learner knows the informal sense of 'grass', but that slang sense may be unknown to many learners.

Etymology

The word supergrass is mainly British slang made from super- ('very' or 'above') and grass ('informer', someone who tells the police). So a supergrass is a very big informer who names many people, which is why it means a witness who gives evidence against a large group of criminals.