Major

adj.hopeful, capableprofessional

What it means

Especially large, important, or consequential within its context.

Reach for it when marking an advance, contribution, decision, or change that materially affects the outcome

Restoring the eastern wetland was a major step in the recovery plan.

everyday
important
when consequence matters more than size
not when Important marks consequence but can understate the large scale implied by major.
everyday
key
when one factor is especially necessary to an outcome
not when Key implies centrality, not necessarily large scale or broad impact.
professional
critical
when success or safety depends on the matter
not when Critical overstates importance if the contribution is valuable but not decisive.
professional
leading
when rank, influence, or prominence within a field matters
not when Leading requires comparison with peers and misfits a large unranked event.
professional
significant
when evidence shows a meaningful effect or importance
not when Significant can be statistical and may refer to a small but reliable effect.
professional
substantial
when amount, size, or evidence is considerable
not when Substantial concerns magnitude and may not mean strategically important.
formal
considerable
for an amount or degree large enough to deserve notice
not when Considerable is measured and can sound weaker than a decisive major change.
formal
far-reaching
when effects extend across many people, places, or later decisions
not when Far-reaching concerns breadth of consequence, not immediate size.
formal
landmark
for a development important enough to mark a turning point
not when Landmark is celebratory and should not label every sizeable improvement.

major achievement
The safe return of the archive was a major achievement for the volunteers.
major contribution
Her major contribution was a method that every clinic could afford.
major improvement
Better ventilation produced a major improvement in the workshop.
major role
Public libraries play a major role in the regional literacy program.

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