'Millstone' in the Bible

No man shall take the mill or the upper millstone to pledge; for he taketh a man's life to pledge.

And a certain woman cast an upper millstone upon Abimelech's head, and brake his skull.

who smote Abimelech the son of Jerubbesheth? did not a woman cast an upper millstone upon him from the wall, so that he died at Thebez? why went ye so nigh the wall? then shalt thou say, Thy servant Uriah the Hittite is dead also.

His heart is as firm as a stone; Yea, firm as the nether millstone.