expression
a tiny amount; a wee bit; to a slight degree
Idiomatic phrase literally meaning 'about the tip of a fingernail', used to emphasize a very small quantity or degree. Often used in negative or humble contexts.
彼の話には爪の先ほどの真実もない。
There isn't even a shred of truth in his story.
爪の先ほどの違いも見逃さない。
I won't overlook even the slightest difference.