WordNet records no synonym and no antonym for kiss of death. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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 ruinous
“if this were known it would be the kiss of death for my political career”
Synonyms, antonyms and the broader and narrower relations for kiss of death come from Princeton University’s WordNet. Full sources and licences.