Scrupulum, meaning a tiny stone (from scrupus sharp stone), indicates a weight of 1⁄24 of a Roman ounce (i.e.) or, by extension, of other measures.
Metaphorically, the stone is thought to be sharp and pricking, like a thorn.
The forms scripulum, scriptulum, scriplus and scriptulus can be found, scriptulum being also associated with the lines on a draughtboard.
Félix Gaffiot: Dictionnaire Illustré Latin Français, Hachette 1934
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