Green’s Dictionary of Slang

new chum n.

[SE new + chum n. ]

1. [early 19C–1950s] (Aus./N.Z./UK Und., also chum, chummy, recent chum) a prisoner just arrived in gaol, on the hulks or in Aus. or N.Z.

2. [mid-19C+] (also chum) a newly arrived and thus inexperienced or naive immigrant (usu. from Britain); also attrib.

3. a novice in any environment .