defence has 16 distinct synonyms spread across 11 of its 11 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 offence.
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.
(psychiatry) an unconscious process that tries to reduce the anxiety associated with instinctive desires
(sports) the team that is trying to prevent the other team from scoring
“his teams are always good on defense”
the defendant and his legal advisors collectively
“the defense called for a mistrial”
an organization of defenders that provides resistance against attack
“he joined the defense against invasion”
the speech act of answering an attack on your assertions
“his refutation of the charges was short and persuasive”
the justification for some act or belief
“he offered a persuasive defense of the theory”
a structure used to defend against attack
“the artillery battered down the defenses”
a defendant's answer or plea denying the truth of the charges against him
“he gave evidence for the defense”
(military) military action or resources protecting a country against potential enemies
“they died in the defense of Stalingrad”
protection from harm
“sanitation is the best defense against disease”
the act of defending someone or something against attack or injury
“a good boxer needs a good defense”
Synonyms, antonyms and the broader and narrower relations for defence come from Princeton University’s WordNet. Full sources and licences.