foolscap
Concise Oxford English Dictionary © 2008 Oxford University Press:
foolscap /ˈfuːlzkap, ˈfuːls-/
▶noun Brit. a size of paper, about 330 × 200 (or 400) mm.
– origin C17: said to be named from a former watermark representing a fool's cap.
'foolscap' also found in these Oxford entries:

