a hair's breadth

The phrase "a hair's breadth" is an idiomatic expression used to describe a very small or minimal distance or amount. It is derived from the literal width of a human hair, which is extremely thin. When something is said to be "a hair's breadth" away or a "hair's breadth" apart, it suggests that there is an extremely tiny or insignificant gap or difference between two things. It indicates a close proximity or a very narrow margin.