Monumental

adj.capable, resilientformal

What it means

Exceptionally great in scale, effort, importance, or lasting consequence.

Reach for it when giving high praise to an achievement or change whose magnitude is genuinely unusual

Restoring the river's natural course was a monumental achievement.

playful
colossal
when extreme physical or figurative size deserves vivid emphasis
not when Colossal can sound comic and says little about value.
everyday
immense
when sheer size or degree is central
not when Immense does not establish importance or lasting consequence.
warm
tremendous
for strong praise of great scale, effort, or effect
not when Tremendous is broad and often promotional.
professional
historic
when an event marks an important change likely to be remembered
not when Historic is overused and requires evidence beyond being large or first.
professional
major
when importance or scale is substantial but not extraordinary
not when Major is more measured and may understate truly exceptional magnitude.
formal
far-reaching
when consequences extend across many areas or years
not when Far-reaching concerns breadth, not the size of the achievement itself.
formal
landmark
when an achievement becomes a reference point for later work
not when Landmark is comparative and may be premature for a recent event.
literary
epochal
when a change defines an era
not when Epochal is an extreme historical claim unsuitable for most achievements.
literary
herculean
when extraordinary effort is the defining feature
not when Herculean emphasizes labor and can romanticize overwork.
literary
towering
when achievement or reputation rises far above peers
not when Towering is comparative and can overcenter one person.

monumental achievement
Completing the accessible trail was a monumental achievement for the small team.
monumental task
Cataloging the damaged archive became a monumental task.
monumental change
Universal voting rights represented a monumental change in public life.
truly monumental
The restoration was truly monumental in both scale and patience.

Monumental is a high claim. Use major or substantial unless scale, effort, or consequence is genuinely exceptional.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.