WordNet records no synonym and no antonym for contributory negligence. 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.
(law) behavior by the plaintiff that contributes to the harm resulting from the defendant's negligence
“in common law any degree of contributory negligence would bar the plaintiff from collecting damages”
Synonyms, antonyms and the broader and narrower relations for contributory negligence come from Princeton University’s WordNet. Full sources and licences.