chum vs chummy

chum is a noun but chummy is not a noun.

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

chum (noun)	chummy (noun)
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

chum (adjective)	chummy (adjective)
	(used informally) associated on close terms
	(used colloquially) having the relationship of friends or pals