keep/play (your) cards close to (your) chest

to not tell anyone what you plan to do.

I never know what Martin's next move will be. He plays his cards close to his chest.

• 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
• claw way
• claw way somewhere
• claw your way
• claw your way back from
• claw your way back from something
• claw your way somewhere
• clean bill of health
• clean break
• Cleanliness is next to Godliness.
• clean out