Definition of ruinous adjective from the Oxford Advanced Learner's Dictionary

     

    ruinous

     adjective
    adjective
    BrE BrE//ˈruːɪnəs//
     
    ; NAmE NAmE//ˈruːɪnəs//
     
    (formal)
     
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  1. 1costing a lot of money and more than you can afford ruinous legal fees They were forced to sell out at a ruinous loss.
  2. 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. 3(formal) (of a town, building, etc.) destroyed or severely damaged a ruinous chapel The buildings were in a ruinous state.
  4. Word Origin late Middle English (also in the sense ‘falling down’): from Latin ruinosus, from ruina, from ruere ‘to fall’.
See the Oxford Advanced American Dictionary entry: ruinous