Small amounts that can be held between thumb and fingers, or tight, painful squeezes of skin.
From Old French 'pincer' meaning to pinch or squeeze. The word has been used since medieval times to describe both the action of squeezing and the small amount you can hold that way.
In cooking, 'a pinch' of salt is actually standardized in modern recipes to mean about 1/16 of a teaspoon—but it started literally meaning whatever you could grab between your fingers! Cooks standardized the 'pinch' so everyone's baking would turn out the same.
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