deaden has 4 distinct synonyms spread across 3 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 enliven.
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.
cut a girdle around so as to kill by interrupting the circulation of water and nutrients
“girdle the plant”
Synonyms, antonyms and the broader and narrower relations for deaden come from Princeton University’s WordNet. Full sources and licences.
make vapid or deprive of spirit
“deadened wine”
lessen the momentum or velocity of
“deaden a ship's headway”
become lifeless, less lively, intense, or active; lose life, force, or vigor
convert (metallic mercury) into a grey powder consisting of minute globules, as by shaking with chalk or fatty oil