enemy has 3 distinct synonyms spread across 2 of its 4 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
an opposing military force
“the enemy attacked at dawn”
an armed adversary (especially a member of an opposing military force)
“a soldier must be prepared to kill his enemies”
any hostile group of people
“he viewed lawyers as the real enemy”
a personal enemy
“they had been political foes for years”
Synonyms, antonyms and the broader and narrower relations for enemy come from Princeton University’s WordNet. Full sources and licences.