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. 2. An old instrument of torture for compressing the thumb by a screw; a thumbkin.
also thumb screw(thumbscrews) 1. A thumbscrew is an object that was used in the past to torture people by crushing their thumbs. N-COUNT 2. If someone puts the thumbscrews on you, they start to put you under extreme pressure in order to force you to do something. N-COUNT