nhôông

Etymology
See.

This particular dialectal form is from the proto-form with, while the dominant form is from  (regular lower register tone due to voiced onset). Although implosives already gave upper register tone, thanks to comparative evidences (🇨🇬 pʰajoːŋ¹), the presyllable can further be recovered. The form with is probably the more original form:, with the non-North Central dialects derived chồng from stage 3 while the North Central form is compatible with stage 2.

Compare also the case of (< ),  (< medial, North Central form, unaffected by lenition) and  (< medial , Northern-Southern form, affected by lenition).