Indispensable means absolutely necessary or impossible to do without. When something is indispensable, you can't accomplish your goal without it. A goalkeeper is indispensable to a soccer team. A good map is indispensable when hiking in unfamiliar mountains. Your best friend might feel indispensable when you're going through a tough time.

You might have dispensable items, things you could give up or replace easily, but indispensable things are the ones you truly need.

When someone becomes indispensable at school or in a group, they've made themselves so valuable and reliable that others depend on them. A student who always remembers to bring the art supplies might become indispensable to their project team. A scientist's careful notes might be indispensable to their research.

Be careful not to confuse this with indisputable, which means something that can't be argued against. Medicine is indispensable for treating illness (you need it), while saying “medicine helps people” is indisputable (no one can argue against it).