- Not in good condition or not reliable
- Not in a good state of physical or mental health
- Affected in a way that changes normal mental function
- Not securely made, positioned, or established
- Not accurate or not based on facts or logic
- The contract was declared unsound due to loopholes in its terms and conditions.
- The building's unsound structure was a threat to the safety of its occupants.
- His unsound actions raised eyebrows, questioning his ability to take rational decisions.