What is the etymology of the word プラスアルファ(+α)?

This is a neologism I believe, however I hear it quite often nowadays. I'm curious to what the origin would be?

2 Answers 2


What is the etymology of the word プラスアルファー

It is usually プラスアルファ, without a long vowel at the end.

It is a compound of two word: プラス + アルファ. プラス is from English "plus". アルファ is thought to have represented a variable x but it was mistakenly identified / read as Greek α and hence アルファ. The intent was "+ x (=something)".

  • Thank you for the correction (updated my question). I'm unfamiliar with the usage "+ x (=something)", is that used in English?
    – Jesse Good
    Jul 10, 2012 at 23:02
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    @Dono Do you have a good reference backing up the origin as a misreading of "+x"? A quick Googling revealed only unsourced hearsay. (Not challenging you on the specifics, just looking for a reliable account of the etymology.)
    – Matt
    Jul 11, 2012 at 1:37
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    I'm with @Matt: the 'mistakenly identified' theory sounds fairly dodgy to me (for a start, why would people mistake a commonly used romaji, for a not so commonly used greek letter??). On the other hand, 'α' is a pretty acceptable variable name for a small, unknown quantity (whereas 'x' would be a more generic unknown).
    – Dave
    Jul 11, 2012 at 1:43
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    @Matt, Dave: Here are quotes from two published references. 『現代カタカナ語辞典\』 (旺文社, 2006):未知数を示すxをギリシャ語のαと見間違えたことから。 And 『大辞泉』(小学館, 2006): アルファは、未知数を示すXをギリシャ語のα(アルファ)に読みまちがえたものという。
    – Dono
    Jul 11, 2012 at 14:14
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    Thanks, @Dono! I'll be keeping an eye out for something more specific myself (if it can be said with such confidence to be a misreading, we should also have documentation of that specific event) but those sources certainly fall on the reliable side of the fence.
    – Matt
    Jul 11, 2012 at 20:49

I asked this same question to my Japanese co-worker the other day and he told me the following reason (although, I'm not entirely convinced)

During baseball in Japan they used to write an X in the 9th inning score box if the team had already won in the 8th inning. This was often written in a shorthand way (1 stroke) which resulted in the X looking like an alpha. From the idea of having done so much more than was needed that they didn't even keep score in the 9th inning - came the associated meaning of doing more than is expected. Just like a baseball team can "プラスアルファ" their score, so can a person "プラスアルファ" an action.

(I'm afraid I have no idea about baseball, so this might not be totally cogent)

  • The wikipedia article I linked to in the comment in the other answer says the same thing. However, there is some debate on whether this is really true or not.
    – Jesse Good
    Jul 13, 2012 at 20:20
  • FWIW, Shogakukan's Kokugo Dai Jiten Dictionary similarly indicates an origin in baseball recordkeeping, where an X used to denote some unknown or unspecified score was misread as an α. May 28, 2014 at 6:24

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