What Is a Grass in British Slang and How Can You Be a Grass?

SING.  domoskanonos/Getty Images

In British underworld jargon, a grass is a criminal insider who snitches on his mates. So, if you've arrived on this page looking for latest on the marijuana situation in the UK, you're going to be disappointed.

"Grass" in British underworld jargon has nothing at all to do with smoking weed. And it's not just a noun; it's an action verb too. If you watch movies about the London criminal subculture or catch a fair amount of British crime drama on television, you've probably come across the word "grass" in various uniquely British uses. Though over time, you may pick up the meaning from the context that surrounds it, the way in which the word grass came to be used in these particular ways is a bit of a puzzle.

Grass as a Noun

A grass is criminal or an insider who informs on his associates. A grass is a rat who 'sings' to the authorities. By extension, it's used by anyone who informs on another over bad or criminal behavior. For example, a teacher trying to discover who is bullying another student might come up against a wall of silence from other teens who don't want to be seen as being a grass or who don't want to grass on their friends.The expression "Supergrass" (also the name of a British band of the 1990s) arose during the Irish "troubles" and was used to describe IRA members who were informers. Today the term Supergrass is still used—usually in newspaper headlines—to describe someone inside major criminal organizations or with information about them.

Grass as a Verb

"To grass" on someone or some group is to be an informer. So if a grass is an informer, to grass, grassing  or grassing up someone describes the act of informing. When you grass on someone or something, you are not only filling the role of informer but also of the betrayer. That's because grassing carries with it the idea that the "grass" is giving information about his close associates (or hers actually, though grass in this sense is rarely used to describe women or girls). If you witness a crime that has nothing to do with anyone you know and then give evidence to the police, you are just a witness, not a grass; you are giving evidence, not grassing. Grassing is about betraying your peers by acting as an informer. The word opens all sorts of other British and underworld slang windows. To grass is to sing like a canary a bird that is yellow - the color of cowards. To grass is considered an act of cowardice amid underworld circles.


The use of grass and "to grass" in this way arose as street argot in the London criminal subculture and dates back to the early part of the 20th century. There are two popular theories about how this came about. One version suggests that it is derived from the expression snake in the grass. That, in turn, actually dates all the way back to the Roman writer Virgil. A more likely possibility, since the usage first arose among the criminal underclass in London, is that it is rhyming slang for "to shop" or "shopper," which have similar meanings (to shop someone is to turn them in to the police).

Follow, if you can, the twisted route through rhyming slang that ends up producing this slang use of grass at its end.

  1. Policemen are often called "coppers" in British slang.
  2. In London rhyming slang, a policeman or copper becomes a "grasshopper".
  3. Someone who turns his pals, or their information over to the police "shops" them to the authorities.
  4. That makes that person a "grass shopper."
  5. Simplify a "grass shopper" and you end up with "grass".

Maybe that's where the word comes from and maybe its origins will remain shrouded in mystery.

Pronunciation: ɡrɑːs, rhymes with ass or the British arse
Also Known As: inform/informer, shop/shopper, betray/betrayer


In 2001, the London Evening Standard reported on an "arch criminal" named Michael Michael who it identified as "Britain's biggest supergrass."

Here's an excerpt from the article, by Paul Cheston, that gets to the heart of what a grass and the act of ​grassing is:

Not only did he inform on some of the most dangerous criminals operating today, he turned in his own mother, brother, wife, mistress and the madam who ran his brothels. And, it was to emerge, he had been "grassing up" his criminal colleagues for years. At his trial he accepted the suggestion he was a "polished liar" and offered the jury this explanation: "Yes, I had to lie, even to my family. It is in the business of informing and dealing ... being disloyal comes with the territory. My friends, family and lover are all awaiting trial because of me."
mla apa chicago
Your Citation
Arfin, Ferne. "What Is a Grass in British Slang and How Can You Be a Grass?" ThoughtCo, Sep. 9, 2021, thoughtco.com/meaning-of-grass-in-british-slang-1661909. Arfin, Ferne. (2021, September 9). What Is a Grass in British Slang and How Can You Be a Grass? Retrieved from https://www.thoughtco.com/meaning-of-grass-in-british-slang-1661909 Arfin, Ferne. "What Is a Grass in British Slang and How Can You Be a Grass?" ThoughtCo. https://www.thoughtco.com/meaning-of-grass-in-british-slang-1661909 (accessed September 26, 2021).