Devastating
Part of speech: adjective
Definition: causing devastation
Part of speech: verb
Definition: To ruin many or all things over a large area, such as most or all buildings of a city, or cities of a region, or trees of a forest.
Example sentence: Regardless of what happens in the markets, stick to your investment program. Changing your strategy at the wrong time can be the single most devastating mistake you can make as an investor.
Destructive
Part of speech: adjective
Definition: Causing destruction; damaging.Causing break down or disassembly.
Example sentence: Guilt is just as powerful, but its influence is positive, while shame's is destructive. Shame erodes our courage and fuels disengagement.