Infirm (adjective)

1. Physically weak or frail.
2. Mentally or emotionally weak or unstable.
3. Not strong or certain.

Origin:

From old french enferme (ill, weak), from latin infirmus (weak, feeble, not strong).

Examples:

1. The infirm elderly man required assistance to walk.
2. He was infirm in his resolve and easily swayed by others.
3. The infirm economy has made it difficult for businesses to survive.
4. The infirm state of the patient made it impossible for him to be discharged.
5. The infirm evidence was not enough to secure a conviction.