Necessity (noun)

1. Something that is needed or required.
2. The state or fact of being necessary.

Origin:

Late middle english: from old french necessite, from latin necessitas, from necesse "necessary".

Examples:

1. Water is a necessity for human survival.
2. The new law made it a necessity for companies to provide health insurance for their employees.
3. The necessity of the situation required them to make a difficult decision.
4. He understood the necessity of hard work and dedication to achieve his goals.
5. The necessity of the repairs became clear after the inspection.