noun (n)

• the state of being weak in health or body (especially from old age)(noun.state)

  Synonym:
  debility, feebleness, frailness, frailty, valetudinarianism
  

  source: wordnet30
• The state of being infirm; feebleness; an imperfection or weakness; esp., an unsound, unhealthy, or debilitated state; a disease; a malady; as, infirmity of body or mind.(noun)

  source: webster1913