scrupulum

Scrupulum is Latin for a small sharp stone, a pebble — the diminutive of scrupus, a rough or sharp stone. The Romans used the word in two ways. Literally, a scrupulum was a tiny stone, the kind that gets inside a sandal and makes every step uncomfortable. Figuratively, a scrupulum was a moral discomfort — a nagging doubt, a prickle of conscience. The metaphor was physical: moral doubt felt like a stone in your shoe.

The apothecaries borrowed the word for their smallest weight unit. A scruple was 20 grains — about 1.296 grams. The connection was size: a scrupulum-weight was about the size of a small stone. Three scruples made a dram, eight drams made an ounce. The apothecary scruple was the base unit for compounding medicines, the weight at which precision began to matter.

English borrowed both meanings simultaneously. The apothecary scruple entered English in the fourteenth century. The moral scruple entered around the same time. Shakespeare used both. A doctor might weigh a scruple of powder. A character might feel a scruple about murder. The pebble in the shoe became the doubt in the conscience and the weight on the scale, all in the same word.

The apothecary scruple disappeared from pharmacy when the metric system replaced apothecary weights in the mid-twentieth century. Prescriptions are now written in milligrams, not scruples. But the moral scruple is alive and well. Having scruples, being unscrupulous, feeling scrupulous — these are common English words. The stone in the shoe survived. The weight on the scale did not.