TB prefixed *m- is more readily interpreted than the stop prefixes analyzed above. With verb roots this prefix has a ‘middle voice’ force, often durative, intransitive, or reflexive. Tibetan m-, as brilliantly interpreted by Wolfenden, represents a ‘neuter’ subject, as opposed to b- andʾ-representing an ‘acting’ subject; cf. mguba ‘rejoice’, mŋa-ba ‘to be, exist’, mnal-ba ‘to sleep’, mtśhi-ba ‘appear, show oneself’, mnab-pa ‘dress oneself’. Prefixed *m- in this role is retained also in Kachin, Bodo-Garo and Kuki-Naga, while Nung replaces this prefix with phǝ-<*bǝ-: phǝsin ‘liver’ <TB *m-sin, phǝlε ‘tongue’ <TB *m-lay. The contrast with TB prefixed *s- is especially clear in the following root; note that the unprefixed root may be either transitive or intransitive, whereas the prefixed *m- form is always intransitive:

(464) T mnam-pa ‘to smell, stink’ (intr.), snam-pa∼snom-pa∼snum-pa ‘to smell’ (tr.), Lepcha nom<*nam ‘to smell’ (intr.), nyom<*s-nam (tr.); Vayu nam ‘to smell’ (tr.), nam-saŋ ‘odor’; Bahing nam ‘to smell’ (tr.), nam-ba ‘having odor’; Miri nam ‘to smell’ (tr.); K nam ‘to taste or smell, as of spices’, mǝnam ‘to smell; smell, scent’ (mǝnam nam ‘to smell offensively’); Nung phǝnam ‘to smell’ (use uncertain); B nam ‘smell offensively, stink’ (intr.), nàm ‘smell, receive scent’ (tr.), ӑnám ‘odor’; Bodo manam ‘to smell’ (intr.); Dimasa maram ‘to stink’ (n<*r through dissimilation); L nam, Ao Naga menem ‘to smell’ (intr.); Tangkhul η∂nam ‘odor’, kh∂η∂nam ‘to smell’ (intr.); Mikir iηnim ‘to smell, be odorous’ (intr.), aηnim ‘odor’, nem-so ‘slight smell, stink’ (-so is diminutive), from TB *m-nam.