Reconstructed for the PEC level. The root obviously meant some odorous grass (cf. "mint" in PL and PN, "hay" in PD, "sweetbrier" in PN), but it is hard to guess the particular species. The comparison involves some metatheses which are only natural in a trisyllabic stem like this. Ultimately the stem can be derived from PNC *HmĭɦwV 'smell, odour' q.v., but it certainly already existed separately in PEC.
The stem was borrowed in some other Caucasian languages: Osset. nūrɨ 'garlic', Georg. niori, Svan. niwra id. (see Abayev 1973, 193).