Related Clues:

• Check on hip
• Control during riding
• Strap to control a horse
• Control, with "in"
• Ha-ha
• Pull back, with 'in'
• Pull back, with "in"
• Conspire internationally to retain control
• Strap held by an equestrian
• Check return of Queen with popular support
• Strap that goes on a bit
• Silver controller?
• It can pull a bit
• One might start with 'Knock knock'
• Apt rhyme for 'constrain'