Green’s Dictionary of Slang

cobber n.2

also cobs, kobber
[? dial. cob, to take a liking to someone or Heb./Yid. chaver, a ‘pal’, a ‘chum’. Like the other great clichéd Aus. word, bonzer adj., cobber is now nearly defunct]

1. [late 19C+] (Aus./N.Z.) a friend, a mate.

2. [1950s] an Australian.

In derivatives

In compounds

cobber-dobber (n.) [dobber n.1 ]

[1960s–70s] (Aus.) one who informs on a friend.