holystone (n.)

soft sandstone used to scrub decks of sailing ships, 1777, despite the spelling, probably so called perhaps because it is full of holes, and thus from hole (n.). The other theory is that it was used for cleaning decks on Sundays. As a verb, by 1828.

Six days shalt thou labor as hard as thou art able
And on the seventh holystone the decks and scrape the cable
["The Philadelphia Catechism," Dana, c. 1830]

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Definitions of holystone from WordNet
holystone (v.)
scrub with a holystone;
holystone the ship's deck
holystone (n.)
a soft sandstone used for scrubbing the decks of a ship;