dullstone
nounUK /ˈdʌl.stəʊn/
US /ˈdʌl.stoʊn/
A dullstone is a rock that is not shiny and does not sparkle.
She picked up a gray dullstone from the path and put it in her pocket.
OTHER MEANINGS
2. A person who is boring and shows little energy or excitement.
Everyone called him a dullstone because he never laughed at any joke.
3. A dull or uninteresting part of something, such as a story or event.
The middle of the movie was a real dullstone, so we almost fell asleep.
4. A stone used for grinding that has lost its sharp, cutting edge.
The old mill could not grind grain well with a dullstone.