feebleness

noun

The condition of being infirm or physically weak: debility, decrepitude, delicacy, delicateness, flimsiness, fragileness, fragility, frailness, frailty, infirmity, insubstantiality, puniness, unsoundness, unsubstantiality, weakliness, weakness. See strong/weak.

The noun has 2 meanings:

Meaning #1: the state of being weak in health or body (especially from old age)
  Synonyms: infirmity, frailty, debility, frailness

Meaning #2: the quality of lacking intensity or substance
  Synonym: tenuity