Wiktionary
adv. (context idiomatic English) By a narrow margin
Usage examples of "by a hair's breadth".
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.
Before they could do so, she took a running jump off the boulder she was perched on, clearing the heads of the bathers below by a hair's breadth and plunging into the tide.
Daniel announced, his voice in Adele's helmet preceding by a hair's breadth its analogue through the ceiling speakers.
I couldn't be sure, but my best guesstimate was that Priscilla was going to lose the race by a hair's breadth.
Costigan's utmost efforts futile to affect by a hair's breadth its line of motion.
He looked down to the first, jutting from the front of his layered armor, a trickle of blood oozing from behind its tip, and knew he had escaped death by a hair's breadth.