\▐ jak\ n [ME Jacke, familiar term of address to a social inferiorm nickname for Johan John] (1548) (1) A blade having high and/or low butts used to actuate the movement of latch knitting needles. (2) Part of a dobby head designed to serve as a lever in the operation of the harness of a loom. (Elsevier's textile dictionary. Vincenti R (ed). Elsevier Science and Technology Books, New York, 1994).