loss has 10 distinct synonyms spread across 4 of its 8 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 gain.
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.
something that is lost
“the car was a total loss”
the act of losing someone or something
“everyone expected him to win so his loss was a shock”
the disadvantage that results from losing something
“his loss of credibility led to his resignation”
the experience of losing a loved one
“he sympathized on the loss of their grandfather”
military personnel lost by death or capture
Synonyms, antonyms and the broader and narrower relations for loss come from Princeton University’s WordNet. Full sources and licences.