mainspring

n 1 principal spring of a clock or watch （钟表的）主发条. 2 (fml fig 文, 比喻) chief motive or reason (for sth) （某事的）主要动机或原因: Her jealousy is the mainspring of the novel's plot. 这部小说情节中贯穿了她的忌妒之心.

mail-order, mailbox, mailed, mailer, mailing list, mailman, mailshot, maim, main, main clause, main deck, main drag, main line, mainbrace, mainframe, mainland, mainline, mainly, mainmast, mainsail, mainstay, mainstream, maintain, maintain contact with, maintenance, maintenance order, maisonette (also maisonnette), maitre d'hotel, maize, Maj, majestic, majestically, majesty, major, major in, major premise, major-general, majority, majority verdict, make,