ずいぶん（ずいぶん、zuibun）
- very/quite

The Japanese word ずいぶん primarily functions as an adverb and expresses the idea of "very," "considerably," "quite," or "a lot." It indicates a significant degree or extent of something. It often conveys a sense of surprise or noticing something more than expected. It is a versatile word, applicable to many different situations. It can also imply "long time" or "a while" depending on the context.

⚫︎ずいぶん寒くなりましたね。 Translation: It's gotten very cold, hasn't it? ⚫︎彼女はずいぶん日本語が上手になった。 Translation: She has become quite good at Japanese. ⚫︎ずいぶん待ったよ。 Translation: I waited for a long time.

⚫︎ Use ずいぶん to emphasize the degree or extent of a quality, action, or state. ⚫︎ It is appropriate in both formal and informal conversations. ⚫︎ It often conveys a sense of noticing or being surprised by something. ⚫︎ It frequently appears with adjectives (e.g., ずいぶん高い - very expensive), adverbs (e.g., ずいぶん早く - very quickly), and verbs (e.g., ずいぶん食べました - ate a lot).

⚫︎ ずいぶん is typically written in hiragana. ⚫︎ It is not usually written in katakana or kanji. ⚫︎ There are no variations in okurigana.

⚫︎ とても (totemo) - very, extremely ⚫︎ かなり (kanari) - quite, considerably ⚫︎ 随分 (zuibun) - (kanji, less common but same meaning) ⚫︎ 大分 (daibun) - (kanji, similar meaning, a bit more formal, or indicating a large amount or time)

⚫︎ There is no direct antonym, as ずいぶん expresses degree. Instead, you might use words that indicate a lesser degree. ⚫︎ 少し (sukoshi) - a little ⚫︎ ちょっと (chotto) - a little bit

ずいぶん前に会ったね。 ・Translation: We met a long time ago, didn't we? ・Explanation: This sentence implies that a significant amount of time has passed since they last met.

ずいぶん変わったね！ ・Translation: You've changed a lot! ・Explanation: This sentence conveys surprise at a noticeable change in someone.

The exact etymology of ずいぶん is not definitively known, but it is believed to be a combination of several elements. The most accepted theory is the term originated as "随分（ずいぶん）," using the kanji characters with the meanings of "as one pleases," "in accordance with," and "ample". However, the kanji are rarely used today.