unsound

Concise Oxford English Dictionary © 2008 Oxford University Press:
unsound/ʌnˈsaʊnd/

▶adjective

• 1 not safe or robust; in poor condition.

  ■ not healthy or well.

• 2 not based on sound evidence or reasoning; unreliable or unacceptable.

  ■ not holding acceptable views.

– derivatives
unsoundly adverb,
unsoundness noun.