-s (2) ending for the mysterious case sometimes called "respective", actually probably a shorter variant of the locative in -ssë. Pl. -is, dual -tes, partitive pl. -lis.
Quenya
-ssë
-ssë
-ssë
suffix. locative ending
-ssë
suffix. abstract noun
-ssë
suffix. himself, *herself, itself
-ssë
respective
-ssë
at
-ssë (1) locative ending (compare the preposition se, sé "at", q.v.); in Lóriendessë, lúmessë, máriessë, yalúmessë (q.v. for reference); pl. -ssen in yassen, lúmissen, mahalmassen, símaryassen, tarmenissen, q.v. Pronouns take the simple ending -ssë, even if the pronoun is plural by its meaning (messë "on us", VT44:12). The part. pl. (-lissë or -lissen) and dual (-tsë) locative endings are known from the Plotz letter only.
-ssë
he loves himself
-ssë (2), 3rd person sg. reflexive ending, melissë "he loves himself", possibly also quernessë *"he turned (himself)" (VT49:20-21). Compare -ttë #2. The ending -ssë* seems prone to confusion with the locative ending; an alternative wording would be the analytical construction melis immo with a separate reflexive pronoun. Tolkien himself changed quernessë to quernes immo **(VT49:20-21).
-s(së)
suffix. he, she, it; him, her, it
-is
respective
-is ending for the plural form of an unidentified case, by some called "respective" or "short locative" (Plotz)
-më
suffix. abstract noun
-rë
suffix. abstract noun
se
at, in
se (2), also long sé, preposition "at, in" (VT43:30; compare the "locative prefix" se- possibly occurring in an early "Qenya" text, VT27:25)
ya
pronoun. which, that (relative pronoun)
The basic relative pronoun in Quenya, mostly used in inflected forms such as: yassen tintilar i eleni “wherein the stars tremble” (LotR/377). See the entry on relative pronouns for further discusion.
Conceptual Development: The use of ᴱQ. ya as a relative pronoun dates back to the Early Qenya Grammar (EQG) of the 1920s (PE14/54), but for a period in the 1930s and 40s ᴹQ. ya was used more as a remote demonstrative (Ety/YA; PE23/96-98). See the entry on correlatives for more on this usage as of 1948.
úpa-
verb. [unglossed]
-ssë (3) possible longer form of the 3rd person ending -s; see -s #1. Such an ending probably could not coexist with -ssë #2 above. In one source, Tolkien first queried, then deleted this ending (VT49:49).