Hair 
In Appalachian and Southern speech, a "hair" is a tiny measurement - the smallest bit you can imagine. It’s used for closeness, precision, or describing how little something is off.
Pronunciation
[HAIR]
Meaning & Usage
- A tiny measurement; the smallest amount (noun)
Mae:
Did it fit?
Did it fit?
Earl:
Yep - off by a hair.
Yep - off by a hair.- Very close; nearly (figurative)
Mae:
Did he win?
Did he win?
Earl:
By a hair.
By a hair.variations: a fraction, a hair’s breadth, a whisker, cut it off by a hair, missed by a hair, he’s a hair taller than me
★ A "hair" is about the skinniest unit of measure you’ll ever hear. Folks use it for cutting boards, tuning engines, and describing close calls: *"missed it by a hair."* ★
Origin and Etymology
From Old English *hǣr* (human hair). Since hair is so fine, it became a natural metaphor for "the smallest possible measure." The phrase "a hair’s breadth" has been in English for centuries, but in Southern and Appalachian speech it became everyday talk.
Usage Notes
Still common in Southern and Appalachian speech, especially in practical work (farming, carpentry, mechanics) and storytelling. Recognized nationally, but in the South/Appalachia it’s a vivid part of everyday talk. See also: mite, smidgen, touch.
Say It Like a Southerner
Said plain: "hair."