enemy vs challenger

enemy and challenger both are nouns.

Word	Noun	Adjective	Verb	Adverb
enemy	Yes	No	No	No
challenger	Yes	No	No	No

As nouns, challenger is a hypernym of enemy; that is, challenger is a word with a broader meaning than enemy:

Other hypernyms of enemy include competition, competitor, contender, rival.

enemy (noun)	challenger (noun)
an opposing military force	the contestant you hope to defeat
any hostile group of people
an armed adversary (especially a member of an opposing military force)
a personal enemy