A noun in The Etymologies of the 1930s glossed “spider” derived from the root ᴹ√SLIG with various other derivatives having to do with webs and fine threads (Ety/SLIG). Most notably it was the second element in the name ᴹQ. Ungoliante “Gloomweaver” (LR/230). In the paradigm of The Etymologies, ᴹQ. ungo was “cloud, dark shadow” (Ety/UÑG), not “spider”.
Conceptual Development: In the Qenya Lexicon and Poetic and Mythological Words of Eldarissa of the 1910s, ᴱQ. liante was glossed “tendril” and was derived from the early root ᴱ√LI+ya “unite many in one” (QL/53, PME/53). In this period it was an element in the name ᴱQ. Ungweliante or Ungwe Lianti “the great spider who enmeshes” (LT1/152), where the intial element ᴱQ. ungwe meant “spider” (QL/98). In the Early Qenya Grammar of the 1920s, ᴱQ. liante was translated “vine” (PE14/55), as opposed to the Qenya Lexicon of the 1910s where ᴱQ. liantasse was “vine” (QL/53).
Neo-Quenya: Tolkien gave no other Quenya words for “spider” in his later writings, but S. ungol was glossed “spider” (Let/180; RC/490, 767) and √ungu- was described as the basis for “spider words” (PE22/160), making it very likely that ✱ungol was “spider” in his later conception of the name Q. Ungoliantë. However, I think [ᴹQ.] liante might be reconceived of as a (feminine?) agental form originally meaning “weaver” or “webspinner”. Furthermore, I think [ᴺQ.] ungol might have come to be associated only with monstrous spiders, the descendants of Ungoliantë, so that [ᴹQ.] liante came to be used of ordinary spiders.
A noun in The Etymologies of the 1930s glossed “fine thread, spider filament” and derived from ᴹ✶ligā under the root ᴹ√SLIG having to do with spider words (Ety/SLIG).
Conceptual Development: The word ᴱQ. lia “twine” appeared in the Qenya Lexicon of the 1910s under the early root ᴱ√LI+ya “unite many as one” with derivatives having to do with threads and vines (QL/53).
Neo-Quenya: In Tolkien’s later writings, √ungu- became the basis for spider words, but I retain ᴹ√SLIG assuming it has to do with threads and twining to salvage words from the 1910s and 30s. As such I’d use lia for threads and cords that are relatively thin compared to other items of their class, especially those crafted by twining: “fine thread”, a “twine” as a thin cord and by extension things like a “✱wire”.