From Longman Dictionary of Contemporary Englishmainspringmain‧spring /ˈmeɪnsprɪŋ/ noun [countable] 1 → the mainspring of something2 TMCthe most important spring in a watch or clock
Examples from the Corpus
mainspring• This double vision of the woman-goddess is said to be the mainspring of Shakespeare's tragedies.• Anticipation is an essential ingredient in good business practice; it is one of the mainsprings that drives a successful business on.• It so happened that the mainspring of my clockwork mouse had broken that very morning.• Kitson's great organizing ability, technical ingenuity, and grasp of industrial developments was the mainspring of these activities.• Also there was the mainspring of the enterprise, the catering team.• The mainsprings of his activity were his religious and political convictions. 