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ruinous

Something ruinous is really terrible or devastating, like a ruinous hurricane that floods your house or the ruinous effect of a new law on a country's poorest citizens.

The adjective ruinous perfectly describes something so bad that it truly causes ruin, "the destruction or disintegration of something." A house fire can be ruinous, and so can a bad hand at a poker table, if the player has bet her last dollar. Ruinous and ruin comes from the Latin root ruina, "a collapse, a rushing down, a tumbling down."

Definitions of ruinous
  1. adjective
    extremely harmful; bringing physical or financial ruin
    “a ruinous course of action”
    synonyms: catastrophic
    harmful
    causing or capable of causing harm
  2. adjective
    causing injury or blight; especially affecting with sudden violence or plague or ruin
    “a ruinous war”
    synonyms: blasting
    destructive
    causing destruction or much damage
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