indispensable

adj. /ˌɪn.dɪˈspen.sə.bəl/ B2

必不可少的；不可或缺的

So good or important that you could not manage without it.

仙境例句

The Rabbit's fan and gloves were indispensable, for he could not see the Duchess without them.

扇子和手套对白兔来说必不可少，因为没有它们，他就不能去见公爵夫人。