'Thumbscrew' definitions:

Definition of 'thumbscrew'

(from WordNet)
noun
Instrument of torture that crushes the thumb
noun
Screw designed to be turned with the thumb and fingers

Definition of 'Thumbscrew'

From: GCIDE
  • 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]