in·dis·pens·a·ble 
(ĭn′dĭ-spĕnsə-bəl)
(ĭn′dĭ-spĕnsə-bəl)adj.
1. Absolutely necessary; essential.
2. Obligatory; unavoidable: the routine but indispensable ceremonies of state.
n.
One that is indispensable.
in′dis·pens′a·bili·ty, in′dis·pensa·ble·ness n.
in′dis·pensa·bly adv.
Synonyms: indispensable, critical, essential, necessary, requisite
These adjectives apply to something that cannot be dispensed with: foods that are indispensable to good nutrition; education that is critical to success; funds essential to completing the project; the necessary tools for the job; lacking the requisite qualifications for the position.
These adjectives apply to something that cannot be dispensed with: foods that are indispensable to good nutrition; education that is critical to success; funds essential to completing the project; the necessary tools for the job; lacking the requisite qualifications for the position.