millstone

noun

1. either of a pair of circular stones between which grain or another substance is ground, as in a mill.
2. anything that grinds or crushes.
3. any heavy mental or emotional burden (often used in the phrase a millstone around one’s neck).

noun

1. one of a pair of heavy flat disc-shaped stones that are rotated one against the other to grind grain
2. a heavy burden, such as a responsibility or obligationhis debts were a millstone round his neck

n.Old English mylenstan, from mill (n.1) + stone (n.). Figurative sense of “a burden” (1720) is from Matt. xviii:6.