Definition of mainspring noun from the Oxford Advanced Learner's Dictionary

     

    mainspring

     noun
    noun
    BrE BrE//ˈmeɪnsprɪŋ//
     
    ; NAmE NAmE//ˈmeɪnsprɪŋ//
     
     
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  1. 1[usually singular] mainspring (of something) (formal) the most important part of something; the most important influence on something Small companies are the mainspring of the British economy. Her Christian faith was the mainspring of her life.
  2. 2the most important spring in a watch, clock, etc.
See the Oxford Advanced American Dictionary entry: mainspring