What is the meaning of unsound?

adjective

• Not in good condition; damaged or decayed.
  • usage: "an unsound foundation"
• Not sound financially.
  • usage: "unsound banking practices"
• Containing or based on a fallacy.
  • usage: "fallacious reasoning"; "an unsound argument"
  • synonyms: fallacious
• Suffering from severe mental illness.
  • usage: "of unsound mind"
  • synonyms: mentally ill, unstable
• Physically unsound or diseased.
  • usage: "has a bad back"; "a bad heart"; "bad teeth"; "an unsound limb"; "unsound teeth"
  • synonyms: bad, unfit
• Of e. G. Advice. .