A noun appearing as {nestor >>} nethron “herd” in the Gnomish Lexicon of the 1910s, clearly derived from the early root ᴱ√NESE “give to feed; feed, pasture; graze” (QL/66) with sr becoming thr.
Neo-Sindarin: The suffix -(r)on is mostly an agental suffix in later Sindarin, so I would adapt this word as ᴺS. nethor “herd, flock” for purposes of Neo-Sindarin from the Neo-Root ᴺ√NES and primitive ✱nes-rē; compare [N.] tathor < ᴹ✶tathrē.
A noun in the Gnomish Lexicon of the 1910s glossed “herd, herdsman, shepherd”, an agental form of G. moth “sheep”, with a variant mastir which is probably the feminine form “✱shepherdess” (GL/56). The gloss “herd” is reinforced by the fact that Tolkien equated it to G. nethron “herd” (GL/60).