The Collaborative International Dictionary
New chum
Chum \Chum\ (ch[u^]m), n. [Perh. a contraction fr. comrade or chamber fellow: cf. also AS. cuma a comer, guest.] A roommate, especially in a college or university; an old and intimate friend.
New chum, a recent immigrant. [Australia]
Wiktionary
new chum
n. 1 (context Australia archaic English) A newly arrived convict. 2 (context Australia English) A beginner, a novice. 3 (context Australia chiefly dated mildly derogatory English) A newly arrived and inexperienced immigrant; a newcomer.