a very narrow margin; a hair's breadth difference; barely different.
勝敗は紙一重だった。
The outcome was decided by a very small margin.
合格と不合格の差は紙一重だった。
The difference between passing and failing was razor-thin.
この二つの案は紙一重で、どちらを選んでも大きな違いはない。
These two plans are a hair's breadth apart; choosing either won't make a big difference.
事故は紙一重で避けられた。
The accident was narrowly avoided.