Adjective ruinous has 2 senses
- catastrophic, ruinous - extremely harmful; bringing physical or financial ruin; "a catastrophic depression"; "catastrophic illness"; "a ruinous course of action"
Antonym: harmless (indirect, via harmful)
- blasting, ruinous - causing injury or blight; especially affecting with sudden violence or plague or ruin; "the blasting effects of the intense cold on the budding fruit"; "the blasting force of the wind blowing sharp needles of sleet in our faces"; "a ruinous war"
Antonym: constructive (indirect, via destructive)
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