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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?

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up vote 6 down vote accepted

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)".

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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 '12 at 23:02
Not really. It is more from math. – Dono Jul 10 '12 at 23:33
@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 '12 at 1:37
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 '12 at 1:43
@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 '12 at 14:14

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)

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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 '12 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. – Eiríkr Útlendi May 28 '14 at 6:24

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