n. 主发条, 主要动机, 主要原因, 主要动力

[法] 主要动机, 主要原因, 主要动力

[ noun ]
the most important spring in a mechanical device (especially a clock or watch); as it uncoils it drives the mechanism
<noun.artifact>

mainspring \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.