mainspring

English Thesaurus

1. the most important spring in a mechanical device (especially a clock or watch); as it uncoils it drives the mechanism (noun.artifact)

hypernym	:	spring,
definition	:	a metal elastic device that returns to its shape or position when pushed or pulled or pressed (noun.artifact)

part meronym	:	clockwork,
definition	:	any mechanism of geared wheels that is driven by a coiled spring; resembles the works of a mechanical clock (noun.artifact)