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.
There isn't even a shred of truth in his story.
I won't overlook even the slightest difference.
Literally 'about the tip of a fingernail' (爪 'nail' + 先 'tip' + ほど 'about, extent'), used idiomatically to indicate a very small amount.