The dictionary definitions for millstone are as follows:
1. Either of a pair of circular stones between which grain or another substance is ground, as in a mill (noun).
2. Anything that grinds or crushes (noun).
3. Any heavy mental or emotional burden (often used in the phrase a millstone around one’s neck ) (noun).
Idiom based on MILLSTONE:
Millstone around one’s neck: A heavy burden, as in Julie finds Grandma, who is crabby, a millstone around her neck . The literal hanging of a millstone about the neck is mentioned as a punishment in the New Testament (Matthew 18:6), causing the miscreant to be drowned. A look at the picture below should illustrate the idea even better.
Usage Examples for MILLSTONE:
1. Left to fight the world alone, with the millstone of her shame around her neck, she had sunk ever lower and lower. -Three Men In A Boat (To Say Nothing Of The Dog) by Jerome, Jerome K.
2. Narmonee took my meaning in an instant, and running out of the house, returned the next moment with a huge rough mass of rock as big as a millstone, and indicated to me that that was exactly the thing I wanted. –Typee by Melville, Herman