indispensable
definition
a person or a thing that you cannot live without, because it is really necessary
example
Minerals are an indispensable part of our lives, as everything from tiny objects to large buildings are made of them.
synonyms
fundamentalcrucialessentialvital
word origin — mid 16th century (in the sense ‘not to be allowed or provided for by ecclesiastical dispensation’): from medieval Latin indispensabilis, from in- ‘not’ + dispensabilis (see dispensable)