DICT.TW Dictionary Taiwan

 main·spring /ˈmenˌsprɪŋ/
 主發條;主要原因

 main·spring n. The principal or most important spring in a piece of mechanism, especially the moving spring of a watch or clock or the spring in a gunlock which impels the hammer. Hence: (Fig.) The chief or most powerful motive; the efficient cause of action; as, the mainspring of action.
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 mainspring
      n : the most important spring in a mechanical device (especially
          a clock or watch); as it uncoils it drives the mechanism