1. causing or likely to cause ruin; extremely destructive or harmful
2. extremely expensive; financially devastating

Examples

• The hurricane had a ruinous effect on the coastal town.
• His gambling addiction proved ruinous to his family’s finances.
• The company’s ruinous spending led to bankruptcy.
• The war’s ruinous impact lasted for decades.
• She avoided the ruinous costs of private school.
• The drought was ruinous for local farmers.
• His ruinous business decisions destroyed the company.