"Chucking his weight about." Self-important. Generally applied to a newly promoted non-commissioned officer or a recruit airing his knowledge.
Chum. An endearing word used by Tommy to his mate when he wants to borrow something or have a favor done.
"Clicked it." Got killed; up against it; wounded.
"Clock." "Trench" for the face.
"Coal Box." The nickname for a high explosive German shell fired from a 5.9 howitzer which emits a heavy black smoke and makes Tommy's hair stand on end.
Coal Fatigue. A detail on which Tommy has to ride in a limber and fill two sacks with coal. It takes him exactly four hours to do this. He always misses morning parade, but manages to get back in time for dinner.
"Cole." Tommy's nickname for a penny. It buys one glass of French beer.
"Coming it." Trying to "put something over."
"Coming the add." Boasting; lying about something.
Communication Trench. A zigzag ditch leading from the rear to the front-line trench, through which reinforcements, reliefs, ammunition, and rations are brought up. Its real use is to teach Tommy how to swear and how to wade through mud up to his knees.