A noun appearing as N. thling “spider, spider’s web, cobweb” in The Etymologies, derived from primitive ᴹ✶sliñgē under the root ᴹ√SLIG (Ety/SLIG).
Neo-Sindarin: Since initial *sl-* became *lh-* in Sindarin, most Neo-Sindarin writers adapt this word as ᴺS. lhing, as suggested in HSD (HSD). This word is somewhat questionable, since in later writings √ungu- was the basis for spider words (PE22/160). However, I think ᴹ√SLIG may be reinterpreted as having to do with threads, and as such I think ᴺS. lhing can be retained, though I would limit its use to “spider’s web, cobweb”, a synonym of nath “web” but descriptive of more diaphanous webs.
A noun for “web” in The Etymologies of the 1930s derived from the root ᴹ√NAT “lace, weave, tie” with Quenya cognate ᴹQ. natse (Ety/NAT).