[usually before noun] a monumental achievement, piece of work, etc is very important and is usually based on many years of work

丰碑式的，伟大的:

a monumental contribution to the field of medicine

对医学领域的重大贡献

Charles Darwin's monumental study, 'The Origin of Species'

查尔斯·达尔文的不朽著作《物种起源》

[only before noun] extremely large, bad, good, impressive etc

极大（坏，好等）的:

Banks and building societies were yesterday accused of monumental incompetence.

银行和购房互助协会昨天被指责极其不称职。

a monumental task

艰巨的任务

There was a monumental traffic jam on the freeway.

高速公路上出现了严重的交通阻塞。

[only before noun] relating to a monument or built as a monument

纪念碑（塔）的; 纪念性的，作为纪念的:

a monumental arch

纪念性拱门