pendulum

noun4

1. •
   A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices such as clocks.
2. •
   The tendency of a situation to oscillate (between two extremes).

   • The pendulum can be seen to be swinging in favour of rail, as with each issue of RAIL comes news of further intermodal service expansion. — 2021
3. •
   A lamp, etc. suspended from a ceiling.
4. •
   A watch's guard-ring by which it is attached to a chain.