failure vs underdog

failure and underdog both are nouns.

Word	Noun	Adjective	Verb	Adverb
failure	Yes	No	No	No
underdog	Yes	No	No	No

As nouns, underdog is a hyponym of failure; that is, underdog is a word with a more specific, narrower meaning than failure:

Other hyponyms of failure include bankrupt, insolvent, flash in the pan, dud, flop, washout.

failure (noun)	underdog (noun)
an act that fails	one at a disadvantage and expected to lose
an unexpected omission
an event that does not accomplish its intended purpose
a person with a record of failing; someone who loses consistently
lack of success
loss of ability to function normally
inability to discharge all your debts as they come due