unsound

Everyday

1. Unsound means not safe or strong; in bad condition, like an unsound building or bridge. tree →
2. Unsound reasoning, ideas or advice are not based on good sense or facts; wrong or unreliable. tree →
3. (law, old-fashioned) «Of unsound mind» means a person who is mentally ill and cannot make responsible decisions. tree →

In the lessons

In safety: an unsound wall, tree or ice can collapse. In maths and logic: an unsound argument gives a wrong conclusion. In law: «of unsound mind». It tells the reader something cannot be trusted.

Examples

• The old bridge was unsound, so it was closed. tree →
• Don't climb that tree – the branch is unsound. tree →
• His argument was unsound because the facts were wrong. tree →
• The ice looked thick but was unsound. tree →
• The engineer said the walls were structurally unsound. tree →
• That plan is financially unsound – it costs more than we have. tree →

Note

Opposite: «sound» (safe, sensible). «Sound» here does not mean noise. «Of unsound mind» is an old legal phrase; today people say a person is unwell.