if something is as regular as clockwork, it happens at exactly regular times.

Her letters arrived every week, regular as clockwork.

• chinless wonder
• Chin up!
• chip in
• chip in something
• chip off the old block
• chip on shoulder
• chip on your shoulder
• chocolate box
• choke off
• choke off something
• choke up
• choke you up
• chop and change
• Chop chop!
• chosen few
• chunk of change
• churn out
• churn something out
• circle the wagons
• claim to fame
• clamp down on
• clamp down on something
• clam up
• clapped-out
• clarion call