Related Clues:

• One casting a "no" vote
• Climactic beginning?
• Like some debaters
• Not a pro
• Picketer, perhaps
• Prefix with proton or ballistic
• Prefix with hero or matter
• Negative prefix
• Opposing side
• One of the opposition
• Apt to say nay
• Opposed one
• Prefix with thesis
• Dissenter's position
• Climax beginning