I've done a bit of digging, and for the life of me, I cannot find any clear record or explanation for why Japanese ココア is pronounced the way it is.
Sources researched to date:
- Lots of different sources at the Kotobank entry for ココア, including Britannica Japan, Daijisen, Kokugo Dai Jiten, MyPedia, Chocolate / Cocoa Dictionary, etc etc.
- Lots of different sources at the Kotobank entry for カカオ
- Chocolate & Cocoa Association of Japan's site
- Snippets from the journal of Tokugawa Akitake (1853–1910), listed as a source on the Chocolate & Cocoa Association's page, wherein Akitake described drinking ココア one morning when visiting the Paris World Fair in 1868, as listed also in the Japanese Wikipedia article about him
Lots of information is out there about カカオ and ココア, and what each of them are, and how the former is turned into the latter. I can confirm in various sources that カカオ is borrowed from Spanish, and ココア is borrowed from English. But I can find nothing about why ココア is pronounced as //ko.ko.a//.
My suspicion is that this is the result of "book pronunciation", based on the English spelling cocoa and simply reading it out vowel-for-vowel. A distant alternative possibility is that the Japanese word somehow metathesized the vowels after borrowing cacao, the common term for this in many other European languages, including the Japanese-contact trifecta of Dutch, Spanish, and Portuguese. English wound up with a pronunciation of //ˈkoʊ.koʊ// (US) or //ˈkəʊ.kəʊ// (UK) not through any metathesis, but rather through early confusion with coco (as in coconut), as best I can tell. (See also the Wiktionary entry.) If ココア were borrowed from spoken English, we'd expect something more like //kóꜜò.kòò//, instead of the //kóꜜ.kò.à// and //kó.kóꜜ.à// pronunciations evident in modern usage.
Does anyone have any solid evidence for why we have this unexpected word form? Or any leads on academics or references that discuss this oddity of etymology?