- Calendar year
- Cant cut the mustard
- Canteen culture
- Carbon footprint
- Carpe diem
- Cast iron stomach
- Cat got your tongue?
- Caught between two stools
- Caught by the short hairs
- Chaise lounge
- Charley horse
- Chasing tail
- Cheek by jowl
- Cherry ripe
- Chew someone out
- Chicken feed
- Childhood
- Children
- Children should be seen and not heard
- China plate
- Chow down
- City bike
- Cliche
- Click bait
- Clock
- Close but no cigar
- Clothes
- Cloud cuckoo land
- Cock and bull story
- Cockney rhyming slang
- Code monkey
- Colour
- Come hell or high water
- Comedy
- Comfort women
- Company man
- Conflict
- Cop an attitude
- Corduroy road
- Country
- Country house hotel
- Crack someone up
- Cream crackered
- Crime
- Cross that bridge when you come to it
- Cross your fingers
- Crunch time
- Cry wolf
- Curiosity killed the cat
- Currant bun
- Cut corners
- Cut to the chase