1. [mid-18C–1930s] to put someone in a position of sharing accommodation, esp. in a prison cell.
2. [mid-18C+] (also chum in, chum it, chum up) to live with, to befriend.
3. [mid-19C+] (also chum in) to join in with.
4. [2000s] to keep a lookout for someone.
1. [late 19C+] to become friendly with.
2. [1910s] (UK Und.) to work as an accomplice with.
[late 19C] to accompany; to travel with.