neither before nor after; no other time; the only time
Used to emphasize that a particular moment or event is unique or the most extreme in one's experience; often followed by a superlative or a statement of exceptional occurrence.
I have never been so scared, neither before nor since.
後にも先にも、彼女に会ったのはその一度きりだ。
That was the only time I ever met her, neither before nor after.