Both Uses of

momentous
in
War and Peace

They went away each on his own account, and yet it was only in consequence of their going away that the momentous event was accomplished that will always remain the greatest glory of the Russian people.†
Chpt 11 *

momentous = of very great significance

and like a child he made sport of the momentous, and unavoidable event—the abandonment and burning of Moscow—and tried with his puny hand now to speed and now to stay the enormous, popular tide that bore him along with it.†
Chpt 11