The principal spring in a mechanical device, especially a watch or clock, that drives the mechanism by uncoiling.(noun)
The chief motivating force: the mainspring of a reform movement. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "mainspring" in a sentence
"When the spiritual stage of her evolution is reached, this occult process must become the whole process; to get through the veil of forces and get at their secret mainspring, which is the Spirit itself, is of cardinal importance."
"Journalism of which the mainspring is the gaining of pleasure may easily degenerate into something akin to the comic actor's function."
"The teacher who can break a mainspring first and keep it from getting mended, is often the most esteemed in the community."