- 1costing a lot of money and more than you can afford ruinous legal fees They were forced to sell out at a ruinous loss.
- 2causing serious problems or damage synonym devastating The decision was to prove ruinous. Such action would be ruinous to her career. a ruinous mistake
- 3(formal) (of a town, building, etc.) destroyed or severely damaged a ruinous chapel The buildings were in a ruinous state.
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