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]

WordNet (r) 3.0 (2006):

jackscrew
    n 1: screw-operated jack [syn: jackscrew, screw jack]