fail vs default

fail is not a noun while default is a noun.

Word	Noun	Adjective	Verb	Adverb
fail	No	No	Yes	No
default	Yes	No	Yes	No

As verbs, default is a hyponym of fail; that is, default is a word with a more specific, narrower meaning than fail:

Other hyponyms of fail include lose track, strike out, default on, choke, muff, miss.

fail (noun)	default (noun)
	loss due to not showing up
	an option that is selected automatically unless an alternative is specified
	loss resulting from failure of a debt to be paid
	act of failing to meet a financial obligation

fail (verb)	default (verb)
stop operating or functioning	fail to pay up
deteriorate
prove insufficient
disappoint, prove undependable to; abandon, forsake
become bankrupt or insolvent; fail financially and close
be unsuccessful
fail to get a passing grade
fail to do something; leave something undone
judge unacceptable
be unable
fall short in what is expected