Related Clues:

• Head-butt, e.g.
• Butters, perhaps
• Piston, essentially
• He's the one for ewe
• Truckers' rest areas?
• Hit broadside, e.g.
• Push firmly
• Metered wheels
• Cabbie's invite
• Aries beast
• 33-Across' mate
• Metered vehicles
• Butter at Fordham
• Broadsides
• Ones going head to head?