What does the word mainspring mean?

Usage examples for mainspring

  1. Fortunately human nature does not readily yield to such behests, and so life is not robbed of its mainspring, and the whole machinery of human nature is not reduced to a chaotic bundle of useless wheels. – The Law-Breakers by Ridgwell Cullum
  2. Now that she was going back, she was without this mainspring of hope- her old studies and pursuits wearied her. – Wife in Name Only by Charlotte M. Braeme (Bertha M. Clay)
  3. 3. A key- note of sincerity should be the mainspring of a well- built speech. – The Century Handbook of Writing by Garland Greever Easley S. Jones