mainspring

The outer end of the mainspring is attached to the rim of the barrel, and the inner end to the barrel arbor.

Unless this double mainspring is known, the conduct of Catherine de' Medici will remain forever misunderstood.

To such religion was the mainspring which kept the whole intellect going; and religion was to be had at the meeting.

All the old restraints were wanting, and self-interest alone formed the mainspring of action.

Fingering is the mainspring, the determining principle, one might almost say the life and soul, of the pianoforte technique.