The horizontal wooden beam running the length of the top of a roof ridge, at which the two sloping sides of the roof meet; the ridge pole of a building.
Origin
Mid 17th century.
Definition of rig-tree in US English:
rig-tree
noun
English Regional, East Midlands, Northern
The horizontal wooden beam running the length of the top of a roof ridge, at which the two sloping sides of the roof meet; the ridge pole of a building.