Hairspring

Part of speech: noun

Definitions

1. A delicate coiled spring in a timepiece that controls the swing of the balance wheel ; a fine curly lock or strand of hair
2. A slender spiral spring inside a watch that regulates its rhythm ; a thin, tightly coiled strand of hair
3. The tiny coiled spring governing a timepiece's balance wheel ; a single fine, curling hair that forms a small spiral

Etymology: A hairspring is a very fine spiral spring, once made of steel and now often of other alloys, that regulates the balance wheel in a watch or clock. The name is a plain compound: "hair" is used for its thinness, and "spring" is the familiar word for an elastic coil that stores and releases energy. Put together, the name describes exactly what the part looks like to the eye, a spring as fine as a strand of hair. The compound is transparent, so nothing about it is hidden or surprising: the object is named by its appearance rather than by any figurative leap. The pattern is typical of technical vocabulary, where ordinary words are combined to name a new small part precisely.