death has 7 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 birth.
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.
the event of dying or departure from life
“her death came as a terrible shock”
the permanent end of all life functions in an organism or part of an organism
“the animal died a painful death”
the absence of life or state of being dead
“he seemed more content in death than he had ever been in life”
the personification of death
“Death walked the streets of the plague-bound city”
the act of killing
“he had two deaths on his conscience”
Synonyms, antonyms and the broader and narrower relations for death come from Princeton University’s WordNet. Full sources and licences.