The Collaborative International Dictionary of English v.0.48:

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.
   [Also spelled hairsbreadth.]
   [1913 Webster]

         Every one could sling stones at an hairbreadth and not
         miss.                                    --Judg. xx.
                                                  16.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hairbreadth \Hair"breadth`\, a.
   Having the breadth of a hair; very narrow; as, a hairbreadth
   escape.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "hairbreadth":
   ace, bit, bowshot, brief span, close quarters, close range,
   closeness, confinement, crack, crowdedness, earreach, earshot,
   gunshot, hair, hair space, hairsbreadth, incapaciousness, inch,
   incommodiousness, limitation, little, little ways, narrow gauge,
   narrowness, nearness, pistol shot, restrictedness, restriction,
   short distance, short piece, short way, slenderness, span,
   spitting distance, step, straitness, strictness, tight squeeze,
   tightness, whisker