thumbscrew

from WordNet (r) 3.0 (2006)

thumbscrew
    n 1: instrument of torture that crushes the thumb
    2: screw designed to be turned with the thumb and fingers

from The Collaborative International Dictionary of English v.0.48

Thumbscrew \Thumb"screw`\, n.
   1. A screw having a flat-sided or knurled head, so that it
      may be turned by the thumb and forefinger.
      [1913 Webster]

   2. An old instrument of torture for compressing the thumb by
      a screw; a thumbkin.
      [1913 Webster]