IPA: /ˈmɪl.stoʊn/
KK: /ˈmɪlˌstoʊn/
A heavy stone used in a mill to grind grain into flour, or something that is a heavy burden or weight.
The old millstone was used for grinding wheat into flour.
Millstone → The word is formed from "mill" (from Old English *mylen*, meaning a place for grinding) and "stone" (from Old English *stan*, meaning a hard substance). A millstone is a stone used in a mill for grinding grain into flour.
Think of a 'place for grinding' ('mill') and a 'hard substance' ('stone') — together, they create a tool used to grind grain.