Tunnel-shaped prefabricated hut made of corrugated steel (protected with various substances including bituminous paints and a patented substance called Arpax) with a cement floor: it was essentially half a cylinder, sometimes with windows like dormers projecting from it. Invented by Lt. -Col. Peter Norman Nissen (1871–1930), it was widely used in the 1914–18 and 1939–45 wars for military use (e.g. offices, barracks, etc.).
OED Supplement (1987)