Infirmity (noun)

1. A physical weakness or ailment.
2. A mental or emotional weakness or instability.
3. A condition or characteristic that impairs or weakens.

Origin:

From old french enfermete, from latin infirmitatem, from infirmus (weak, frail).

Examples:

1. His infirmity made it difficult for him to walk.
2. The infirmity of old age made it difficult for him to take care of himself.
3. Her infirmity made her dependent on others.
4. The infirmity of the economy was causing widespread unemployment.
5. The infirmity of the evidence made it difficult to build a solid case.