Pinch

As much of a dry substance as can be taken up between the thumb and forefinger.

The pinch is more precise than it sounds. Apothecaries used it as a recognised quantity, and it appears in pharmacopoeias as a fraction of a scruple, while modern American measuring spoon sets are sold with a pinch marked at an eighth of a teaspoon. Like the gowpen and the handful, it is defined by the body rather than by a vessel, which means it varies between people and nobody minds: it is used where the difference between slightly more and slightly less does not matter. Its smaller sibling, the smidgen, is conventionally half a pinch, and a dash sits above it at around an eighth of a fluid ounce for liquids. All three are used in recipes with a confidence out of all proportion to their definition.