Definition:Apothecaries' Weights and Measures/Mass/Scruple/Linguistic Note

Linguistic Note on Scruple
The word scruple is derived from the Latin scrupulus, which means small sharp stone.

A scruple in contemporary language means pang of conscience, probably deriving from the irritation given by a small stone in one's footwear.

Hence ones scruples are loosely understood as things that one does not do, as a result of one's sense of personal decency.

The phrase he would not scruple to ... is interpreted to mean his conscience would not prevent him from ..., usually in the context of performing some act generally considered socially unacceptable.