mainspring
/ˈmeɪnˌsprɪŋ/
noun
- The most important cause or motivating force behind something.
- Her desire to help others was the mainspring of her charity work.
- Curiosity is the mainspring of scientific discovery.
- Profit was the mainspring of their business decisions.
- The principal spring in a mechanical device, especially a clock or watch, that drives the mechanism.
- The watchmaker replaced the broken mainspring.
- Without its mainspring, the old pocket watch would not run.
- A wound mainspring stores energy to power the clock.