Cruck

Crucks: 1) Pair of curved timbers extending from ground to roof ridge supporting wall and roof of a building. (Kenyon, John R. Medieval Fortifications, 211)

2) Primitive truss formed by two main timbers, usually curved, set up as arch or inverted V. Each cruck is called a blade, and a pair may be cut from the same tree. (Wood, Margaret. The English Medieval House, 411)