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