by a hair

by a hair('s breadth)

 and by a whisker
Fig. just barely; by a very small distance. I just missed getting on the plane by a hair's breadth. I made it onto the last flight by a hair!
See also: hair

by a hair

Also, by a hairbreadth or whisker . Very narrowly. For example, His serve was out by a hair, or We made our flight by a hairbreadth, or Dad missed hitting the pole by a whisker. The first two hyperboles for the very narrowest margin date from the 1300s and 1400s respectively; whisker meaning "a small amount" was first recorded in 1913. Also see by the skin of one's teeth; hang by a hair.
See also: hair
References in periodicals archive ?
I have to give the nod to Hospital A by a hair, primarily because of those nice nurse assistants.