Are "ピーナッツ" and "ピーナツ" both correct for "peanut(s)"?

Question

I've just noticed that the usual word for "peanut" or "peanuts" in Japanese is "ピーナッツ" (pīnattsu), but the first spelling I found, from looking in the translation table in the English Wiktionary was actually "ピーナツ" (pīnatsu).

It turns out the first one has its own entry while the second one is just a redlink in the English entry's translation table. But both seem to get plenty of Google hits.

Are they both correct? Might they have slightly different usages, such as in combining forms or singular vs plural?

Since I'm asking, there is also 落花生{らっかせい}. Is it no longer used in favour of the English-derived term?

Answer 1

Searching the Balanced Corpus of Contemporary Written Japanese (BCCWJ) gives the following results:

ピーナツ　　　１１６件
ピーナッツ　　１８８件

So it seems like the latter is somewhat more common. All of these results are drawn from contemporary sources, and although ピーナッツ is more common, ピーナツ is common enough that I think, descriptively speaking, both spellings should be considered correct.

Looking through the corpus results, I don't see any obvious patterns in usage. Both spellings seem to be used interchangeably. I don't see any reason to consider them separate words.

Out of curiosity, I decided to search for ドーナ(ッ)ツ:

ドーナツ　　　２３２件
ドーナッツ　　９３件

It's interesting that here, the trend is toward the shorter spelling. But again, I don't see any obvious patterns in usage to suggest that they should be considered separate words.

So in short, the most common spellings for the two words appear to be ピーナッツ and ドーナツ, but the other spellings seem to be common enough that I'd say they're variants rather than misspellings.

Answer 2

大辞泉 has

ピーナツ
(「ピーナッツ」とも) ラッカセイの実。南京(ナンキン)豆。

ピーナッツ
=> ピーナツ.

but I think that ピーナッツ is a more modern spelling, respecting that ピーナッツ is related to ナッツ (ナツ is not a valid transcription of "nut(s)"). I checked with my trusted Japanese cuisine expert, and her verdict is that nobody really writes ピーナツ anymore. (Her recipe( book)s all contain ピーナッツ.)

落花生 has a much longer entry and is about the whole plant. In my experience, 落花生 (when it means the "nut") is often used for 国産 peanuts (or the same variety of peanuts, but produced in China). All foreign products, whether made from Japanese or foreign peanuts, usually have ピーナッツ (or ピーナツ) in their name, e.g. ピーナツバター, ピーナツ・オイル, etc.