A rough, prickly husk around the seeds or fruit of some plants.
Any of several plants having such husks.
A rotary cutting implement having a selection of variously shaped heads.
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.