loser vs contestant

loser and contestant both are nouns.

Word	Noun	Adjective	Verb	Adverb
loser	Yes	No	No	No
contestant	Yes	No	No	No

As nouns, contestant is a hypernym of loser; that is, contestant is a word with a broader meaning than loser:

loser (noun)	contestant (noun)
a gambler who loses a bet	a person who participates in competitions
a contestant who loses the contest	a person who dissents from some established policy
a person with a record of failing; someone who loses consistently