unsound

not in good condition; damaged or decayed

• “an unsound foundation”

not sound financially

• “unsound banking practices”

containing or based on a fallacy

• “fallacious reasoning”
• “an unsound argument”

suffering from severe mental illness

• “of unsound mind”

physically unsound or diseased

• “has a bad back”
• “a bad heart”
• “bad teeth”
• “an unsound limb”
• “unsound teeth”

of e.g. advice

in deplorable condition

• “a street of bedraggled tenements”
• “a broken-down fence”
• “a ramshackle old pier”
• “a tumble-down shack”