A millstream is a small river or stream that flows into or out of a mill.
A millstream can make people think of old-fashioned mills, the countryside, and the sound of flowing water.
Examples:
The millstream flows past the old mill.
We can hear the sound of the millstream from here.
The millstream is full of fish.
The millstream is like a long, skinny lake.
The millstream is the fastest river in the world!
The millstream is a good place to catch fish.