/ ˈruːɪnəs; NAmE / adjective ( formal )
1.
costing a lot of money and more than you can afford :
ruinous legal fees
2.
causing serious problems or damage
SYN devastating :
The decision was to prove ruinous.
3.
( formal ) ( of a town, building, etc. ) destroyed or severely damaged :
a ruinous chapel
The buildings were in a ruinous state.
► ruin·ous·ly adverb :
ruinously expensive
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WORD ORIGIN
late Middle English (also in the sense falling down ): from Latin ruinosus , from ruina , from ruere to fall.