dead has 14 distinct synonyms spread across 8 of its 21 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 3 recorded opposites are alive, live, living.
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.
no longer having or seeming to have or expecting to have life
“the nerve is dead”
not showing characteristics of life especially the capacity to sustain life; no longer exerting force or having energy or heat
“Mars is a dead planet”
(followed by `to') not showing human feeling or sensitivity; unresponsive
“passersby were dead to our plea for help”
a time when coldness (or some other quality associated with death) is intense
“the dead of winter”
completely and without qualification; used informally as intensifiers
“an absolutely magnificent painting”
9 of the 21 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for dead.
Synonyms, antonyms and the broader and narrower relations for dead come from Princeton University’s WordNet. Full sources and licences.