pentathlon vs athletics

pentathlon and athletics both are nouns.

Word	Noun	Adjective	Verb	Adverb
pentathlon	Yes	No	No	No
athletics	Yes	No	No	No

As nouns, athletics is a hypernym of pentathlon; that is, athletics is a word with a broader meaning than pentathlon:

Other hypernyms of pentathlon include athletic competition, athletic contest.

pentathlon (noun)	athletics (noun)
an athletic contest consisting of five different events	an active diversion requiring physical exertion and competition
	participation in sports events as an extracurricular activity
	a contest between athletes