ADJ-GRADED 重大的;关键的;有影响的 If you refer to a decision, event, or change as momentous, you mean that it is very important, often because of the effects that it will have in the future. 重大的;关键的;有影响的
...the momentous decision to send in the troops.
派遣部队的重大决定
The past three years have been among the most momentous in world history.