a very shortdistance or a very small amount (as is the width of a hair)
1597, William Shakespeare, The Merry Wives of Windsor (Act IV, Scene 2)I see you are obsequious in your love, and I profess requital to a hair's breadth;
Dickens Little Dorrit|1|30... it was characteristic of this man, as it is of all men similarly marked, that whatever he did, he overdid, though it were sometimes by only a hairsbreadth...
1919, John Buchan, Mr. StandfastWe've missed our shot by a hairsbreadth and that's the same as missing by miles.
2010, Neil McDonald, Quadrant, March 2010, No. 464 (Volume LIV, Number 3), Quadrant Magazine Limited, page 100:In Avatar the spectacular rides to the rescue and hairsbreadth escapes have the whole film behind them and because of that are dramatically and emotionally satisfying.