/ ˌmɒnjuˈmentl; NAmE ˌmɑːn-/ adjective
1.
[ usually before noun ] very important and having a great influence, especially as the result of years of work
SYN historic :
Gibbon's monumental work 'The Rise and Fall of the Roman Empire'
2.
[ only before noun ] very large, good, bad, stupid, etc.
SYN major :
a book of monumental significance
We have a monumental task ahead of us.
It seems like an act of monumental folly.
3.
[ only before noun ] appearing in or serving as a monument :
a monumental inscription / tomb
a monumental mason (= a person who makes monuments )