Indispensable

adj.capable, resilientprofessional

What it means

So necessary or useful that the intended result is hard to achieve without it.

Reach for it when giving strong praise to a contribution with a specific essential function

Local translators were indispensable during the emergency health campaign.

everyday
essential
the thing is plainly required for the result
not when Essential lacks the appreciative force carried by indispensable.
warm
invaluable
usefulness is exceptionally high even if substitutes exist
not when Invaluable praises worth but does not literally mean impossible to do without.
warm
vital
success, safety, or survival depends strongly on it
not when Vital can overstate a useful contribution when failure would still be possible.
professional
crucial
one factor has decisive importance at a key point
not when Crucial can be temporary, whereas indispensable often describes continuing need.
professional
necessary
a requirement should be stated without praise
not when Necessary is functional and may sound grudging when honoring a person.
formal
foundational
later work depends on an underlying contribution
not when Foundational can remain important after the original contributor is no longer needed.
literary
irreplaceable
no substitute would preserve the same personal or distinctive value
not when Irreplaceable centers uniqueness, not operational necessity.

indispensable role
Community nurses played an indispensable role in restoring trust.
indispensable tool
A simple field notebook became an indispensable tool for the surveyors.
prove indispensable
Her knowledge of the old pipes would prove indispensable during the repair.

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