The Collaborative International Dictionary
Hairbreadth \Hair"breadth`\ (-br[e^]dth), Hair's breadth \Hair's" breadth`\ (h[^a]rz"-). The diameter or breadth of a hair; a very small distance; sometimes, definitely, the forty-eighth part of an inch.
Every one could sling stones at an hairbreadth and not
miss.
--Judg. xx.
16.
Wikipedia
A hair's breadth, or the width of human hair, is used as an informal unit of a very short length. It connotes "a very small margin" or the narrowest degree in many contexts.
Until the middle of the 20th century, the highest resolution of measurement was considered to be the same order of magnitude, around 10 metres, as the diameter of a human hair. A "hair's breadth" was, and still is, informally, a very small measurement.
Usage examples of "hair's breadth".
He picked out the leading Caproni in the third flight, hoping his attack would spoil the bomb-layer's aim, and he touched left rudder and rotated the Hurricane's nose downwards a hair's breadth until the silver and blue Caproni swam gently in the rose of his gunsight.
He lifted Xhia on tiptoe by his scrotum, then made the gesture of drawing the blade across the stretched sac, almost touching the skin, but shaving past it by a hair's breadth.
At that point, he simply leaned toward the scorpion-man, letting the blade pass within a hair's breadth of his head, yet 1 sensed no concern or urgency from him.
The Consortium won't budge a hair's breadth and the workers have mocked his efforts, he has nightmares of a bloodbath one day soon, there's too much hate, too much fear, the place is too polarized.
The last time I'd been aboard a Serenissiman vessel, I'd come within a hair's breadth of being beheaded.
The snake's striking head missed the fast-retreating fingers by less than a hair's breadth.
She could not give up normal food, or be immune to cold or heat, or sleep on mold and dust in airless places, or pass as I do through a hair's breadth chink.
The anguish did not leave his eyes and his voice was hoarse and strained, but his hands did not vary the course of the speedster by so much as a hair's breadth.
It seemed to him they were a hair's breadth from locating Bin Nedrach.