stone weight for pickle tub cover
A heavy stone placed on the lid of a pickle tub (漬物桶) to press down the contents during fermentation.
祖母は漬物桶の蓋の上に重し石を置いた。
My grandmother placed a stone weight on the lid of the pickle tub.
Compound of 重し (weight) and 石 (stone). The exact historical derivation is uncertain, but the word transparently describes a stone used as a weight.