1. impossible to capture, enter, or overcome by force
Usage: often used of fortifications or defensive positions
2. unable to be defeated or refuted
Usage: figurative use

Examples

• The castle’s impregnable walls had never been breached in centuries of warfare.
• The mountain fortress seemed impregnable from every angle of attack.
• Her impregnable logic left no room for counterargument.
• The team built an impregnable defense that allowed only two goals all season.
• His impregnable reputation in the scientific community was built over decades.
• The impregnable security system protected the bank’s vault.
• Despite numerous attempts, the enemy found the position impregnable.