indispensable adj.
VERBS be, prove | become | make sb/sth He had soon made himself indispensable. | consider sb/sth
ADV. absolutely | almost, virtually
PREP. for Written sources are considered virtually indispensable for today's history teaching. | in These drugs are almost indispensable in the fight against the disease. | to skills which turned out to be indispensable to her career
You can also check other dicts: indispensable (English, 中文解释 ), wordnet sense, Collins Definition