stump
Definitions
The part of a tree or plant remaining in the ground after the trunk or stem has been cut off.
To be unable to find an answer or solution to a problem or question.
A short, thick, or blunt end remaining after something has been broken off or worn down.
Examples
The old oak tree was cut down, leaving only a jagged stump in the middle of the yard.
The difficult math problem managed to stump even the brightest students in the class.