Salut,
Grass est déjà un mot anglais qui signifie cela selon Antidote : « any of a variety of very common plants with narrow green leaves and stems growing from a base, eaten by cows, horses, sheep, etc »
Also, in an old-fashioned, slang it means marijuana.
Finally, informally, it means « someone, usually a criminal, who tells the police about other criminal activities and plans »
J'espère t'avoir aidé et bonne journée! ;)