In general, inNẫu dialects, the monophthongs/e/ and/ɛ/ in mainstream dialects at final position shifted to/əː/ (mainstreamquê vs. Nẫuquơ,để vs.đở,ghê vs.gơ) and/iə/ (xe vs.xia,té vs.tía, unless preceded by the glide/w/:khoẻ vs.phẻ) respectively. Yet in this case, Nẫu/iə/ corresponds to mainstream/e/, not/ɛ/. Since the etymological vowel of this item was originally/e/, this iconic Nẫu form most likely indicates an irregular shift of/e > ɛ/.
dìa