Call down
Curse someone / something

Call of nature
Need to go to toilet

Call the roll
Call out to check the total number

Can a duck swim?
An Ironic question to ask someone who say something stupid.

Can of worms
Something anyone don't want to be involved.

Can't get a word in edgeways
Have no chance to say anything

Can't make head nor tail
Cannot understand something

Can't take a chance
Can't take a risk

Carrot and stick
A combination of good and bad/ positive and negative.

Carry a big stick
Carry so much power or authority.

Cat got a tongue            
Can't speak / talk (for any reasons)

Catch some rays
Walk/ sit under the sun

Caught between two stools
You have to choose between two difficult options

Chance it
Take a risk / Take a chance to try

Chip on the shoulder
Still angry from something in the past

Cold Sweat
Feel very nervous of something

Come in handy
Become beneficial

Come off
Succeed

Come to pass
Happen / Occur

Confide in
Trust someone enough to tell the secret or personal story

Cost an arm and a leg
Extremely expensive

Count on
Trust / Reply on

Count towards
Approve that something is correct / becomes effective

Cut corners
Buy unacceptable quality products/services to save money