Middle English scriple "a unit of weight," from Latin scrupulus "small sharp stone"
from early French scrupule "scruple," from Latin scrupulus "scruple, a small sharp stone"
Word Origin
Having a sharp pebble in your shoe can be painful enough to keep you from walking until you remove it. That fact was well known by the ancient Romans, who regularly wore sandals. Scruple comes from the Latin word scrupulus, which originally meant "a small sharp stone." The ancient Romans also used scrupulus to refer to a feeling or thought that might keep a person from doing something that was not quite right. It seemed to them to affect the conscience in the same way that a tiny stone in the shoe would keep a person from being able to walk. This second meaning of scrupulus is the one that still survives in our English word scruple.