cobber vs chum

cobber and chum both are nouns.

Word	Noun	Adjective	Verb	Adverb
cobber	Yes	No	No	No
chum	Yes	No	No	No

As nouns, chum is a hypernym of cobber; that is, chum is a word with a broader meaning than cobber:

Other hypernyms of cobber include brother, buddy, crony, pal, sidekick.

cobber (noun)	chum (noun)
Australian term for a pal	a large Pacific salmon with small spots on its back; an important food fish
	bait consisting of chopped fish and fish oils that are dumped overboard to attract fish
	a close friend who accompanies his buddies in their activities