From The Collaborative International Dictionary of English v.0.48 :
Jackscrew \Jack"screw`\, n.
A jack in which a screw is used for lifting, or exerting
pressure. See Illust. of 2d Jack, n., 5.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
jackscrew
n 1: screw-operated jack [syn: jackscrew, screw jack]