indispensable.

So necessary that a purpose cannot reasonably be achieved without it.

Use it for

Words that belong together

• indispensable resource
• indispensable to research

On the page

Local knowledge proved indispensable to the survey.

Usage notes

Primary category: academic / formal. Forms: Comparative more indispensable; superlative most indispensable when comparison is meaningful. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings. Established modern English lexical item. No separate regional spelling or grammatical inflection entry. Writing functions: analysis, evaluation. Commonness: moderately common.