1. the quality or state of being mountainous; the characteristic of having many mountains or being full of mountains
Usage: formal; rare
2. the quality of being very large, steep, or difficult to traverse, as mountains are
Usage: figurative; rare

Examples

• The mountainousness of the terrain made the expedition extremely challenging.
• Hikers were impressed by the mountainousness of the landscape in the national park.
• The mountainousness of the Alps has shaped European geography for millennia.
• Despite the mountainousness of the region, settlements thrived in the valleys.
• The mountainousness of the task ahead seemed insurmountable at first.