n.
重大, 重要性

[ noun ]
utmost importance
<noun.attribute>

Momentous \Mo*men"tous\, a. [Cf. L. momentosus rapid,
momentary.]
Of moment or consequence; very important; weighty; as, a
momentous decision; momentous affairs. -- {Mo*men"tous*ly},
adv. -- {Mo*men"tous*ness}, n.

momentousness \mo*men"tous*ness\ n.
utmost importance.
[WordNet 1.5]