torsion pendulum

noun Horology.
  1. a pendulum the weight of which is rotated alternately in opposite directions through a horizontal plane by the torsion of the suspending rod or spring: used for clocks intended to run a long time between windings.

Origin of torsion pendulum

First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018