millstone

n. either of a pair of heavy circular stones between which a grainy substance is ground, grindstone; emotional weight, burden

Millstones or mill stones are used in windmills and watermills, including tide mills, for grinding wheat or other grains.Millstones used in Britain were commonly of two types:Derbyshire Peak stones of grey millstone grit, cut from one piece, used for grinding barley; imitation Derbyshire Peak stones are used as decorative signposts at the boundaries of the Peak District National Park. Derbyshire Peak stones wear quickly and are typically used to grind animal feed since they leave stone powder in the flour making it undesirable for human consumption.French burr stones, used for finer grinding. Not cut from one piece, but built up from sections of quartz, cemented together with plaster, and bound with iron bands. French Burr comes from the Marne Valley in northern France.
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Noun
1. (figurative) something that hinders or handicaps; "she was an albatross around his neck"
(synonym) albatross
(hypernym) hindrance, deterrent, impediment, balk, baulk, check, handicap
2. any load that is difficult to carry
(hypernym) load, loading, burden
3. one of a pair of heavy flat disk-shaped stones that are rotated against one another to grind the grain
(hypernym) stone
(part-holonym) gristmill

(n.)
One of two circular stones used for grinding grain or other substance.
  

Synonyms and related words:
bale, burden, burdening, burthen, cargo, charge, charging, cheese grater, comminutor, crusher, cumber, cumbrance, deadweight, drag, duty, encumbrance, freight, granulator, grater, grinder, handicap, incubus, incumbency, kominuter, lading, levigator, load, loading, masher, mill, mortar and pestle, nutmeg grater, onus, oppression, overload, overtaxing, overweighting, pestle, pressure, pulverizer, quern, quernstone, rock crusher, roller, saddling, shredder, steamroller, superincumbency, surcharge, task, tax, taxing, triturator, weight