The Lord of the Rings, Appendix D mentioned aurë and lómë as the
Quenya words for day and night, though this particular piece of
information was omitted from the revised edition. In any case, aurë
reappeared in chapter 20 of the Silmarillion, Fingon crying
utúlie’n aurë, the day has come, before the Nirnaeth Arnoediad
(Húrin following up with aurë entuluva, day shall come again,
when the battle was lost). The Silmarillion Appendix, entry ur-
heat, be hot, defines aurë as sunlight, day. In the
Etymologies, the stem ur- be hot was struck through (LR:396), but
Tolkien must have restored it later: The word Urimë (or Úrimë) as
a name of the month of August, occurring in LotR, Appendix D, is clearly
to be derived from this stem, and the entry ur- in the
Silmarillion Appendix confirms this. The word aurë was however not
listed in the Etymologies even while the stem ur- persisted there. The
added a in aurë must be seen as an example of a-infixion, parallel
to the process that results in such primitive forms as thausâfoul
from the stem thus- (LR:393) or taurâmighty from tur- (LR:395). In
Quendi and Eldar, Tolkien stated that words formed by a-infixion
"were mostly intensive, as in…[Quenya] tauravery mighty, vast,
of unmeasured might or size (*tur). Some were continuative, as in
VaireEver-weaving (*wir)" (VT39:10). In the case of a root like
ur-, a-infixion of course cannot be distinguished from a-prefixing,
since there is no initial consonant. Whether the resulting stem *aur- is
to be seen as "intensive" or "continuative" is a matter of taste; the
period of daylight is perhaps perceived as "continually hot" when
compared to the colder night. The complete primitive word day must be
either *aurê (since the ending -ê may be used to derive words
for abstract or intangible things) or *auri (compare primitive ari
as the source of Q areday in LR:349 s.v. ar1-). Ilaurëa shows a
prefix il- that can safely be referred to the stem il- all
(LR:361). The same source provides an example of the prefix il-
every-; it occurs as part of the word ilqaeverything (better
spelt ilqua according to Tolkien’s later system). WJ:372 also has
ilqueneverybody (incorporating -quenperson). #Ilaurë
thus means everyday as a noun (though this may not necessarily exist
as an independent word); to this form the adjectival ending -a has
been added to produce ilaurëadaily, of every day. This word
is somewhat similar to amaurëa, said to be a poetic word for
dawn, early day (MC:223). While this also seems to incorporate
aurëday, the ending -a is apparently not adjectival here,
unless this is actually an adjective that is also used as a noun.
Ilaurëa in any case belongs to the part of speech that we would
expect. – For the purpose of dating, it is interesting that the word
aurëday is included in the text before us. While a word auresunlight, sunshine, goldlight, warmth had appeared
already in the Qenya Lexicon of 1915 (QL:33), this word as a term for
day arose relatively late in Tolkien’s conception and apparently does
not predate the LotR Appendices. (In the "Qenya" of the 1915 Lexicon,
the words for day are kala of daylight as opposed to night, and lú
of a full 24-hour cycle [QL:44, 56] – but in later Quenya, these words
reappear with the much more general meanings light and occasion,
respectively.) As indicated above, in the Etymologies of the
mid-thirties the Quenya word for "day" had been are (LR:349 s.v.
ar1), and this word was still valid in Tolkien’s early drafts for the
LotR Appendices: In PM:127 we have a reference to "the Eldarin day or
arë". When Tolkien first coined such a word as mettarë,
mentioned in Appendix D as the last day of the year, he may well have
thought of this as a compound mettaend + arëday. Then it
seems that for some reason he rejected ar1 as the stem yielding words
for "day". Perhaps wishing to keep such compounds as mettarë
unchanged, he introduced the Elvish word ré (LotR, Appendix D: "a
day of the sun they called ré and reckoned from sunset to sunset").
Now mettarë could be re-explained as mettaend + ré(24-hour)
day, the long é naturally being shortened at the end of a compound.
The earlier word are survived as áresunlight, mentioned in
Appendix E as the older name of Tengwa No. 31. But here it is also said
that áre was earlier áze, indicating that Tolkien now thought of
the original stem as as, not ar as it had been in the Etymologies:
The sound r was no longer perceived as original, but arose from
original s (via z). For a stem as, see the entry arien in the
Silmarillion Appendix; cf. also such a post-LotR source as MR:380,
where it is said that the name of the sun was originally Âs, "which
is as near as it can be interpreted Warmth, to which are joined Light
and Solace". MR:380 also mentions Ázië, "later" Árië, as the
name of the spirit of the sun, displaying the same development (s >)
z > r as in áze > áre. But these revisions in Tolkien’s
conception necessitated further changes. In earlier editions of LotR,
Appendix D quoted the Sindarin word for day (used of a full 24-hour
cycle) as aur. This superficially agrees with the Etymologies,
where the Noldorin/Sindarin word for day or morning had likewise
been given as aur (LR:349). By the time Etym was written, this aur
was probably perceived as the cognate of Quenya áradawn (for Quenya
long á corresponding to Noldorin/Sindarin au, cf. for instance Q
nárflame being the cognate of N/S naur, LR:374 s.v. nar1-).
Sindarin aurday, as quoted in Appendix D in earlier editions of
LotR, could similarly have been the cognate of the Quenya word áresunlight that is mentioned (as the name of a Tengwa) in Appendix E –
if Tolkien had not changed the stem from ar to as. In Sindarin, r
cannot come from earlier s; nothing like the development s > z >
r occurs in Sindarin (or the Noldorin of the Etymologies). So if
Tolkien wanted to keep aur as the Sindarin word for day (and he
clearly did), a new etymology had to be sought; aur could not be
referred to the new stem as that had replaced ar. Hence Tolkien instead
decided to derive aur from the (already invented) stem ur having to do
with heat, evidently envisioning an a-infixed (or a-prefixed)
variant *aur as outlined above: Here the sound r was original and
simply remained unchanged in Sindarin. However, this derivation brought
up the question of whether there might not be a Quenya cognate – and
this, it seems, is how the Quenya word aurëday arose. Since
this word refers to "day" only in the sense of "daylight", it could very
well coexist with the new word ré, that means "day" in the sense of
a full 24-hour cycle. The word aurë with the meaning day thus
evidently does not predate the LotR, and the fact that it is
incorporated in the adjective ilaurëa in the text before us, probably
places this text in the post-LotR period (after the book was written,
but not necessarily before it was published).