a rafter having less than the full length of the roof slope, as one meeting a hip or a valley.
Origin of jack rafter
First recorded in 1750–60
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for jack rafter
a short rafter used in a hip roof
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012