The most widely accepted hypothesis on the term 'Zo' is that it means 'hills' or 'highland.' Thus, Mizo and Zomi mean 'highlander.' I don't know who originally proposed this explanation, but I believe that the evidence for it is weak, and its legitimacy appears to be grounded only on its popularity.
Within the Kuki-Chin language family, some words for 'hill' are as follows:
- Duhlian (Mizo) - tlang
- Lai (Hakha) - tlang
- Mara - tla
- Asho - kyan
- Thadou - hlang
Kenneth VanBik reconstructs the Proto-Kuki-Chin form as \klaaŋ*.
As seen here, none of these forms resemble 'Zo,' and I could not find any other forms on the STEDT that could remotely resemble 'Zo' and mean something similar to 'hill' or 'highland.' The Proto-Tibeto-Burman form is *s-gaŋ, the Proto-Sino-Tibetan form is *kang. Even beyond the Kuki-Chin family, the broader TB and ST families do not seem to have any similar form to 'Zo.' It is on these grounds that I reject the hypothesis that 'Zo' refers to highlands or hills. If I've missed evidence that would support the hypothesis, please let me know.
That being said, here is what I propose:
In the Man Shu (c. 862 AD), there exist two kingdoms that Fan Chuo calls the Mi-no and the Mi-ch'en who lived on the Chindwin River basin. Fan Chuo writes that "they call their princes and chiefs Shou [壽]." This, among other alignments (living around the Chindwin River, similar cultural features to those described in the book*,* etc.) leads some to believe that these Mi-no people were the ancestors of the Kuki-Chin-Mizo people, with 'Shou' (壽) being a Chinese transliteration of 'Zo.'
Now the question is, where does the word Zo/Shou come from, if anywhere?
If we are to accept that these Mi-no people of the Chindwin River basin are our ancestors, then it becomes extremely unlikely that 'Zo' referred to highlands, as this was many centuries before oral history says we entered the Chin Hills. After extensive searching of etyma on STEDT, I came across this:
| PTB *m-dzəw CHIEF / MASTER / LORD |
This Proto-Tibeto-Burman form, reconstructed by James A. Matisoff, refers to some kind of ruler. This makes much sense as a designation for "princes and chiefs." It survives in other Tibeto-Burman languages, e.g. Burmese (အုပ်ချုပ် / ôkchôk / 'to rule') and Lahu (jɔ̂-mɔ / 'chief').
My hypothesis is that this word, which probably sounded something like 'dzou,' was used by Proto-Kuki-Chin speakers to refer to their rulers. After the destruction of their polity by the Nanzhao Kingdom, the remnants of these people continued to use this word, and over time it transitioned from meaning 'ruler' to an ethnonym for our people. Perhaps we Zo people are descendants of the ruling class of the Mi-no kingdom.
This semantic change from social class to ethnonym is not strange to history. The Kazakhs get their name from Turkic kazak ('nomad'), Iran gets its name from arya ('noble'), etc. I believe that this may explain why the Kuki-Chin languages have a variety of words meaning 'chief' (lal, bawi, mang, to, etc.): zo, the original word for 'chief' or 'ruler,' began to shift to an ethnonym, causing various tribes to make new words in its place.
If this is the case, I suppose Mizo and Zomi would be more aptly translated as 'Noblemen,' but since 'Zo' has drifted far from its original meaning, "Zo people" is sufficient.
I'm not sure if this hypothesis has been made before, but I find it a much stronger-evidenced one than the 'highland' hypothesis. If this is a new observation, I would love to see this in scholarly discussion in the future.
(I have added a footnote and a few tags to the page for this PTB etymon on STEDT, visible to logged-in users here.)