grass up - definition and synonyms

phrasal verb [transitive] British informal
present tense
I/you/we/theygrass up
he/she/itgrasses up
present participlegrassing up
past tensegrassed up
past participlegrassed up
  1. to tell someone in authority, especially the police, about something bad that someone else has done

    You wouldn’t grass up an old mate, would you?

    Who grassed him up to the police?

See also main entry: grass