fingerbreadth vs finger's breadth

fingerbreadth and finger's breadth both are nouns.

Word	Noun	Adjective	Verb	Adverb
fingerbreadth	Yes	No	No	No
finger's breadth	Yes	No	No	No

As nouns, fingerbreadth and finger's breadth are synonyms defined as:

fingerbreadth and finger's breadth: the length of breadth of a finger used as a linear measure

Other synonyms of fingerbreadth include digit, finger.

fingerbreadth (noun)	finger's breadth (noun)
the length of breadth of a finger used as a linear measure	the length of breadth of a finger used as a linear measure