Validity (noun)

1. The state or quality of being valid or acceptable.
2. The state or quality of being well-grounded or justifiable.
3. The state or quality of being legally or formally recognized as effective.

Origin:

Late middle english: from old french validite, from latin validitas, from validus "strong, powerful".

Examples:

1. The validity of the argument.
2. The validity of the evidence.
3. The validity of the contract.