Once; one time (casual speech).
いっぺん会って話したい。
I want to meet and talk with you once.
その店にはいっぺん行ったことがある。
I've been to that shop once.
いっぺん試してみる価値はある。
It's worth trying at least once.
Used after a noun as a suffix meaning exclusively; only; just (colloquial).
正直一遍言ってみなさい。
Just tell me honestly once.
義理一遍の付き合いならやめた方がいい。
If it's only an obligation-based relationship, it's better to stop it.