defensive has 3 distinct synonyms spread across 2 of its 3 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 offensive.
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.
intended or appropriate for defending against or deterring aggression or attack
“defensive weapons”
attempting to justify or defend in speech or writing
an attitude of defensiveness (especially in the phrase `on the defensive')
Synonyms, antonyms and the broader and narrower relations for defensive come from Princeton University’s WordNet. Full sources and licences.