fallen angel
1. An angel who has rebelled against God and has been subsequently cast out of heaven. The Bible describes Lucifer as having become a fallen angel after he desired to become God rather than be a servant of God.
2. In finance, a stock or bond that has drastically declined in value. Try to avoid investing in fallen angels—they may have been highly priced once, but they will never return to their original value.
3. A company or organization that was previously successful but is currently failing. The high school's debate team was this year's fallen angel, losing all of their competitions after being dominant last year.