brother vs cobber

brother and cobber both are nouns.

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

As nouns, cobber is a hyponym of brother; that is, cobber is a word with a more specific, narrower meaning than brother:

brother (noun)	cobber (noun)
a male with the same parents as someone else	Australian term for a pal
a male person who is a fellow member (of a fraternity or religion or other group)
a close friend who accompanies his buddies in their activities
used as a term of address for those male persons engaged in the same movement