1. A condition of damage or decay
   "The unsoundness of the old wooden beams made the building unsafe"
    
2. A misconception that is fallacious and not true or valid
   "the unsoundness of his conclusion was obvious"
    
3. Not mentally or physically healthy
   "no one can be a poet without a certain unsoundness of mind"

Type of: bad, badness, condition, misconception, status

Antonym: soundness, wisdom