What does "hairsbreadth" mean?

Alternative form of hair's breadth: a very short distance or a very small amount (as is the width of a hair).

What is a synonym for "hairsbreadth"?

Common synonyms include: hair's breadth, ace, approach, barely, bit, closeness.

Pronounced //ˈhɛəɹzbɹɛdθ//.

/ˈhɛəɹzbɹɛdθ/ noun

noun ·Moderate ·College level

Noun

1
Alternative form of hair's breadth: a very short distance or a very small amount (as is the width of a hair). alt-of, alternative
"[...] I ſee you are obſequious in your loue, and I profeſſe requitall to a haires bredth, [...]"
2
a very small distance or space wordnet

"The speeding car missed the child, who ran out into the road, by only a hairsbreadth."

From hair + -s- + breadth.