ruinous

/ˈruənəs/

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