Related Clues:

• ABC, to 14-Down
• Close competitor
• Macduff, to Macbeth
• Nearby school, maybe
• Very tough thing to lick
• Old enemy
• Traditional foe
• Unconquerable foe
• Frenemy, maybe
• Monopolist's lack
• Mudslinging target
• Adversary or foe
• Greek goddess of retribution
• Challenger, competitor
• Adversary, antagonist