an enemy / an opponent, a competitor / (historical) the other party in a lawsuit / 的: (historical) in the red-light district, a term of reference used between prostitutes and customers

an enemy / revenge, vengeance / opponent (of the game or conflict) / (archaic, obsolete) marriage partner

的: (historical) (by extension from the red-light district usage) term of third-person reference: that guy, that one

enemy / foe

to rival

(software, Internet) spyware

industrial spy

(colloquial) current boyfriend

everything

(slang) Alternative form of 彼氏 (kareshi, “boyfriend”)