say it: ROO-uh-nuhs
ruinous is an adjective meaning "extremely harmful; bringing physical or financial ruin". It carries 2 recorded senses.
extremely harmful; bringing physical or financial ruin
“a catastrophic depression”
“catastrophic illness”
“a ruinous course of action”
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”
Definitions, synonyms and semantic relations for ruinous come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.