by a hair/whisker

by a hair/whisker

Very narrowly, by a very small distance or amount. For example, “He missed sideswiping that car by a hair,” or “That ball was in, but just by a whisker.” Both versions of this cliché allude to the fineness of a single hair. The first, also put as by a hairbreadth, dates from the fourteenth century, whereas the second originated in early twentieth-century America.
See also: by, hair, whisker