Ruinous (adjective)

1. Causing great harm or destruction; disastrous.
2. Extremely costly, financially or otherwise.

Origin:

From the latin word ruina, meaning "a fall or collapse" which is derived from the verb ruo meaning "to fal.l"

Examples:

1. The war had a ruinous effect on the economy.
2. The company's financial mismanagement resulted in ruinous losses.
3. The storm caused ruinous damage to the city.
4. The company's reputation suffered ruinous blow after the scandal.
5. The delay had a ruinous effect on the project's timeline.