potter's field
A place where the indigent or the unknown are buried. A reference to the Bible, "So they conferred together and bought the potter's field with it as a burial place for foreigners" (Matthew 27:7). Primarily heard in US. The work was so grueling that a great number of immigrant laborers who built the railroads across this country ended up in some potter's field or another before the job was complete.
potter's clay
A special type of clay that does not contain iron and is often used for making pottery. OK, class, make sure to get some potter's clay before you sit down at your wheel today.