jack rafter

Webster's Dictionary (1913)

Architecture, in England, one of the shorter rafters used in constructing a hip or valley roof; in the United States, any secondary roof timber, as the common rafters resting on purlins in a trussed roof; also, one of the pieces simulating extended rafters, used under the eaves in some styles of building.

From the entry Jack.

Webster’s Revised Unabridged Dictionary (1913), from GCIDE 0.54