
Millstone
Historical Tool
Understand that 'millstone' refers to an old milling technology; it's not used in modern contexts except historically. 
Literal Use
'Millstone' is rarely used in a literal manner today, but when it is, it's referring to the actual stone. 
Hand Grinding
Smaller versions, called 'querns', were used by hand and can also be referred to as 'millstones' in some contexts. 