bitter enemy

• adversaryEnemy in conflict
• nemesisPersistent source of ruin
• foeHostile opponent
• rivalOne who competes against
• archenemyPrincipal antagonist

sworn · hatred · vendetta · grudge · feud · antagonist · mortal · opponent · hostile · vengeance · loathing · resentment · spite · animosity · betrayal · clash · warfare · revenge

• revengeretaliation, payback, vengeance, vendetta, blood feud