Answer:
A morbidlyยญ-named body of water
Thousands lay up gold within this house, But no man made it. Spears past counting guard this house, But no man wards it.
Lighter than what I am made of, More of me is hidden Than is seen.
A horrid monster hides from the day, with many legs and many eyes. With silver chains it catches prey. And eats it all before it dies. Yet in every cottage does it stay. And every castle beneath the sky.
A tiny bead, like fragile glass, strung along a cord of grass.
What is so fragile that saying its name breaks it?