noun, adverb
Used as a noun or adverb meaning a single occurrence. Often appears in casual speech.
See also: 一遍に
いっぺんだけ会ったことがある。
I've met him just once.
いっぺんに全部はできないよ。
I can't do it all at once.
noun, used as a suffix
Attaches to nouns to mean 'nothing but' or 'solely'. Common in set phrases like 正直一遍 (nothing but honesty) or 義理一遍 (just out of obligation).
彼のやり方は義理一遍で、心がこもっていない。
His way of doing things is just perfunctory, with no real feeling.
あの人は正直一遍で、融通がきかない。
That person is nothing but honest and lacks flexibility.