civilian has no recorded synonym. 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 2 recorded opposites are serviceman, military.
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.
a nonmilitary citizen
associated with civil life or performed by persons who are not active members of the military
“civilian clothing”
Synonyms, antonyms and the broader and narrower relations for civilian come from Princeton University’s WordNet. Full sources and licences.