yassë (2) adv. "once upon a time" (YA); writers may rather use yalúmessë or yáressë of similar meaning to avoid confusion with # 1 above.
Quenya
yassë
in which
yassë
once upon a time
yassen tintilar i eleni
in which twinkle the stars
The 6th phrase of the prose Namárië, essentially unaltered from its poetic form:
> yassen tintilar i eleni (“in which twinkle the stars”)
It seems that Tolkien left this phrase in the “poetic” word order despite its inclusion in the “prose” version of the poem. In normal Quenya word order, the subject precedes the verb:
> yassen tintilar i eleni »»» ✱yassen i eleni tintilar (“in which the stars twinkle”)
This (hypothetical) word order is consistent with the English translation of the poetic version: “wherein the stars tremble”.
Alternately, this example may indicate that even in ordinary Quenya speech, the subject could be displayed to after the verb in a subordinate clause. It seems unlikely this was a universal rule, since there are attested examples where this did not happen:
yá hríve menë, ringa ná “when winter comes, it is cold” (VT49/24)
náner ataformaitë ve fírimor quetir “✱they were ambidextrous as mortals say”
yassen tintilar i eleni
wherein the stars tremble
Last part of the sixth line @@@
yáressë
once upon a time
yáressë noun in locative "once upon a time" (locative form of yárë) (YA)
-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.
ya
which, what
ya (1) relative pronoun "which, what" (attested in VT43:28, 34 and in the Arctic sentence), with locative suffix in Namárië: see #yassë. According to VT47:21, ya is impersonal, "which" rather than "who(m)" (compare the personal form ye). The dative form yan (q.v.) is however used for "to whom" (rather than "to which") in one text, indicating that Tolkien did not always distinguish between personal and impersonal forms. In the phrase lúmessë ya [variant: yá**] firuvammë, "in [the] hour that we shall die", the relative pronoun is not explicitly marked for case and is evidently understood to share the case of the preceding noun (hence not lúmessë yassë**... "in [the] hour in which"...) (VT43:27-28) Presumably, ya has the plural form *yar* (e.g. i nati yar hirnen** "the things that/which I found").
ya
pronoun. which, that (relative pronoun)
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)
yalúmessë
once upon a time
yalúmessë noun in locative "once upon a time" (locative form of yalúmë) (YA)
#yassë (1) relative pronoun in locative "in which", pl. yassen referring back to a plural noun (relative pronoun ya + locative ending) (Nam, RGEO:66)