1 staggering, awe-inspiring, outstanding, prominent, stupendous, vast, awesome, epoch-making, historic, history-making, memorable, lasting, permanent, unforgettable, significant, notable, noteworthy, impressive, marvellous, prodigious, wonderful, wondrous, spectacular, magnificent, grand, striking, glorious, enduring, classic:
This work is a monumental contribution to linguistic theory.
2 massive, huge, gigantic, enormous, prodigious, colossal, immense, vast, tremendous:
These monumental stones, each as big as a house, were dragged from a quarry hundreds of miles away.
3 commemorative, memorial:
A monumental obelisk will be raised to mark the battle.
4 egregious, catastrophic, calamitous, huge, enormous, awful, abject, terrible, unforgivable, unbelievable, monstrous, Colloq whopping:
Announcing our plans in advance could prove to be a monumental blunder.