A noun appearing as G. ostor “enclosure, circuit of walls” in the Gnomish Lexicon of the 1910s, an elaboration of G. ost¹ “enclosure, yard; town” (GL/63).

Neo-Sindarin: Since S. ost “citadel, (fortified) town” continued to appear in later Sindarin, I think this word might be retained as ᴺS. ostor “enclosure, circuit of walls, *town wall” for purposes of Neo-Sindarin.