feebleness
1. [ noun ] (medicine) the state of being weak in health or body (especially from old age)
Synonyms: debility infirmity frailness frailty
Related terms: unfitness asthenia cachexia enfeeble
2. [ noun ] the quality of lacking intensity or substance
Synonyms: tenuity
Examples:

"a shrill yet sweet tenuity of voice"- Nathaniel Hawthorne

Related terms: weakness