millstone
Pronunciation:
/ˈmɪlstəʊn//ˈmɪlˌstoʊn/noun
Definitions
A large round stone used for grinding grain.
A coarse-grained sandstone used for making such stones; millstone grit.
Often in a millstone round one's neck (referring to Matthew 18:6 in the Bible): a heavy responsibility that is difficult to bear.
Example: Paying the mortgage every month is a millstone round their necks.