sidekick vs chum

sidekick and chum both are nouns.

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

As nouns, sidekick and chum are synonyms defined as:

sidekick and chum: a close friend who accompanies his buddies in their activities

Other synonyms of sidekick include brother, buddy, crony, pal.

sidekick (noun)	chum (noun)
a close friend who accompanies his buddies in their activities	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