The story
From fascine + knife, from one use of such knives which was to cut wood for fascines and gabions (“cylindrical wicker baskets or cages filled with earth or stones and used in fortifications, etc.”).
Etymology from Wiktionary, CC BY-SA 4.0.
fascine knife
fasc·ine knifeToday it means: A large, heavy knife or short sword used by 17th- to 19th-century artillery and infantry soldiers as a sidearm and a tool for cutting fascines (“cylindrical bundles of small sticks of wood, used for strengthening purposes”) and other things. Full definition →