Quote:
"The moraic nasal existed in Old Japanese only in words borrowed from Chinese." (
Japanese: A Linguistic Introduction, Yoko Hasegawa)
JapaneseA simple example would be 天. It was pronounced something like /tʰen/ or /tʰien/ in Middle Chinese and would've been borrowed into Old Japanese most likely with the pronunciation /tʲeN/ (compare Vietnamese
thiên and Korean
cheon), which eventually became /teN/ by Middle Japanese.
Internally, Japanese itself saw many nasal-vowel syllables (typically with a high vowel) reduce to a moraic nasal by either Early Middle Japanese or Late Middle Japanese. A classical example is how /jomi-/ "read" + /-te/ became /joNde/ 読んで. There are also limited examples of /N/ originating from voiced labial consonants, e.g. /tobi-/ "fly" + /-te/ became /toNde/ 飛んで.
Still an active process dialectallyThe process of nasal-vowel syllable reduction is still active in some dialects. For example, in the
Kagoshima dialect, it's so pervasive that nearly all /ni/, /nu/, /mi/ and /mu/ syllables have become /N/. For example, /kamu/ "to bite" and /kami/ "hair" are both /kaN/ in this dialect.
RyukyuanAnd just in case you're curious, all Ryukyuan varieties also have /N/ both in borrowed Chinese words and in native words and verbs, so it's certain that the sound change started before the Ryukyuan varieties split off from mainland Japanese.
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Chances are it's Ryukyuan (
Resources).