Definitions

1. noun

a small iron bar with a screw thread on one end, used to press or tighten something by turning the other end, often used as a torture device

“The medieval knight used a thumbscrew to extract information from the prisoner.”

2. noun

a device with a screw thread and a handle, used for pressing or tightening something, often used in engineering or manufacturing

“The engineer used a thumbscrew to adjust the pressure in the hydraulic system.”