indispensable
absolutely necessary; impossible to do without
Roots
- -able / -ible: able to be, fit to be, or worthy of
- im- / in- (not): not or without
- pend / pens: hang, weigh, lean, or be suspended
Other words with the pend / pens root
Indispensable means you cannot dispense with it. Remove it, and the plan no longer works.
Sleep became indispensable once she realized tired practice was teaching her mistakes.
The helpful memory is the phrase dispense with. If you can dispense with something, you can do without it. If it is indispensable, you cannot.
The living phrase is clearer than the older root machinery here: indispensable means too necessary to dispense with.