hair's-breadth vs hairsbreadth

hair's-breadth and hairsbreadth both are nouns.

Word	Noun	Adjective	Verb	Adverb
hair's-breadth	Yes	No	No	No
hairsbreadth	Yes	No	No	No

As nouns, hair's-breadth and hairsbreadth are synonyms defined as:

Other synonyms of hair's-breadth include hair, whisker.

hair's-breadth (noun)	hairsbreadth (noun)
a very small distance or space	a very small distance or space