A millstone is a large, flat, round stone which is one of a pair of stones used to grind grain into flour.
PHRASE
重担;重负;累赘
If you describe something as a millstone or a millstone around your neck, you mean that it is a very unpleasant problem or responsibility that you cannot escape from.
例句
For today's politicians, the treaty is becoming a millstone...对于今天的政客而言，这个条约正在变成一个包袱。That contract proved to be a millstone around his neck.那个合同结果成了他的一个负担。