ruinous
UK: ˈruːɪnəs | US: ˈruːɪnəs
adj. causing or likely to cause ruin; disastrous
adj. in a state of ruin; dilapidated
adj. extremely wasteful or extravagant
The word "ruinous" derives from the Latin ruina (meaning "a collapse" or "destruction"), which passed into Old French as ruine before entering Middle English. The suffix -ous (from Latin -osus) denotes "full of" or "characterized by," turning the noun "ruin" into an adjective. The logical progression reflects something "full of ruin," whether physically (e.g., a crumbling building) or metaphorically (e.g., disastrous consequences).
The earthquake left the city in a ruinous state.
His ruinous spending habits led to bankruptcy.
The war had a ruinous effect on the economy.
The castle stood as a ruinous reminder of past glory.
Policies with ruinous consequences were swiftly abandoned.