The full sentence is: 彼はクラスで一番頭がいいと勘違いしている。

The part I'm not understanding is: 一番頭がいい

  • 2
    It means "the most intelligent". Commented Nov 3, 2016 at 17:03
  • can you provide a more detailed explanation? Commented Nov 3, 2016 at 17:10
  • Recommended search: jisho.org/search/%E9%A0%AD%E3%81%8C%E3%81%84%E3%81%84
    – Christer
    Commented Nov 3, 2016 at 17:10
  • 1
    Please explain what parts you understand, also what parts of 一番頭がいい you may understand.
    – Earthliŋ
    Commented Nov 3, 2016 at 20:03
  • to my english brain it reads like: number one head good, and that doesn't make sense to me. Commented Nov 3, 2016 at 20:35

2 Answers 2


(The comment section has sorted this out, but just to summarize the whole thing,)

「頭がいい」 is an idiom (慣用句) that means bright/intelligent. 「一番」 is literally number one, and from there it means best/top/most/first. 一番 is strictly speaking a noun, so from that perspective this should be 一番に頭がいい by inserting a particle, but this particle often gets dropped, and 一番 can work like an adjective, just like "best."

So the whole sentence translates to "He wrongly thinks he is the brightest in this class."


「[一番]{いちばん}X」, with X an adjective, means "the most X" (literally, "the first [in a ranked list] X").

This is a casual (though polite) way to say this, and the formal way is 「[最]{もっと}もX」. Besides, there are adjectives that are already superlatives, that you might come across with:

the highest
the newest
the best, the most appropriate

These adjective are actually rather frequent, so you might want to give it a look.

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