enemy vs contender

enemy and contender both are nouns.

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

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

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

enemy (noun)	contender (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