British & Australian old-fashioned, informal to become friends with someoneoften + with
Alice chummed up with Jenny and they often walked to school together.The boys chummed up while on holiday.
phrasechum up chum upold-fashioned to become friends with someone+ withLani soon chummed up with the girl in the room next door.■ SIMILAR TO: pal up BrE informal
chum up
To be friendly with someone. Why is Patrick chumming up to me all of a sudden? He's usually so distant.