semifinalist vs challenger

semifinalist and challenger both are nouns.

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

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

semifinalist: one of four competitors remaining in a tournament by elimination
challenger: the contestant you hope to defeat

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

semifinalist (noun)	challenger (noun)
one of four competitors remaining in a tournament by elimination	the contestant you hope to defeat