failure has 4 distinct synonyms spread across 2 of its 7 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is success.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an act that fails
“his failure to pass the test”
an event that does not accomplish its intended purpose
“the surprise party was a complete failure”
a person with a record of failing; someone who loses consistently
an unexpected omission
“he resented my failure to return his call”
inability to discharge all your debts as they come due
“the company had to declare bankruptcy”
loss of ability to function normally
“kidney failure”
Synonyms, antonyms and the broader and narrower relations for failure come from Princeton University’s WordNet. Full sources and licences.