nen noun "river" (LT1:248), "river, water" (LT1:262) (In Tolkien's later Quenya, nén with a long vowel means "water", but hardly "river" - that is sírë.)
Quenya
nén
noun. water, water, [ᴱQ.] river
nen
river
nén
water
nén (nen-) noun "water" (NEN).
Nénar
water
Nénar noun name of a star (or planet), evidently derived from nén "water" (Silm), tentatively identified with Uranus (MR:435)
nén-talma
wet flat
nén-talma noun Quenya cognate of Sindarin nindalf "wet flat" = Wetwang (PE17:52, 167)
Uinen
water
Uinen (Uinend-, as in dative Uinenden) fem. name, used of a Maia, spouse of Ossë (UY, NEN). Adopted and adapted from Valarin (WJ:404), though it is also said that it contains -nen "water" (SA:nen); the latter explanation may be folk etymology. In the Etymologies, the name is derived from the same stem (UY) as uilë "long trailing plant, especially seaweed".
celusindi
river
celusindi _("k")_noun "river" (LT1:257; hardly a valid word in Tolkien's later Quenya, where the terms sírë and sirya appear instead)
hlóna
river, especially given to those at all seasons full of water from mountains
[hlóna (2) noun "a river, especially given to those at all seasons full of water from mountains" (VT48:27; the word is marked with a query and the note containing it rejected; it was apparently replaced by lón, q.v.)]
nuinë
suffix. river
sindi
river
sindi noun "river" (LT1:265; rather sírë in LotR-style Quenya)
sirya
river
#sirya noun "river", attested in the dual form siryat (VT47:11). Compare sírë.
sír
river
sír noun "river", shorter form of sirë (PE17:65, VT49:17)
sír(ë)
noun. river, river, [ᴱQ.] stream
The most common Quenya word for “river”, derived from the root √SIR “flow”.
Conceptual Development: This word first appeared as ᴱQ. sīre “stream” as a derivative of ᴱ√SIŘI [SIÐI] (QL/84), and this form and gloss also appeared in the contemporaneous Poetic and Mythological Words of Eldarissa (PME/84). The form ᴹQ. siri- “river” appeared in the Declension of Nouns (DN) from the early 1930s, along with uninflected sire with short i and various inflected forms with siry- (PE21/10). The form sīre “river” with long ī appeared in The Etymologies of the 1930s as a derivative of ᴹ√SIR “flow” (Ety/SIR; EtyAC/SIR). In several notes from the mid-1960s, it appeared in monosyllabic form sír (PE17/65) or sīr (VT49/17), but it had dual form siryat from the late 1960s implying a stem form of sirĭ- and a development similar to that of DN from the early 1930s (VT47/11).
Neo-Eldarin: Its form síre is probably better known and more commonly used in Neo-Quenya. For example this is the typical form in Helge Fauskanger’s NQNT (NQNT).
sírë
river
sírë noun "river" (SIR, VT46:13), "stream" (LT1:265). Also short form sír, q.v.Compare #sirya.
The word for “water”, a derivative of the root √NEN of the same meaning (PE17/52; Ety/NEN). Its stem form was nen- (Ety/NEN) and its primitive form was given as ✶nē̆n, the vowel length variation due to distinct subjective nēn versus objective/inflected nĕn- in ancient monosyllables (PE21/64).
Conceptual Development: This word first appeared in the Qenya Lexicon of the 1910s with two senses: “river” and (archaic) “†water”. Tolkien indicated the two senses were based on distinct roots: ᴱ√NEŘE [NEÐE] and ᴱ√NENE respectively, with two distinct stem forms nend- and nēn (QL/64-65). The Poetic and Mythological Words of Eldarissa also mentions the forms nen (nēn-) “water” versus nen(d-) “river” (PME/64-65). In the English-Qenya Dictionary of the mid-1920s Tolkien had both nēn “river” (PE15/76) and nēn “water” (PE15/78), but in the Early Qenya Grammar he had only nēn “water” (PE14/43, 72), also appearing as nen “water” in documents on The Valmaric Script from this period (PE14/110).
In the Declension of Nouns from the early 1930s, Tolkien had ᴹQ. nēn “water”, but in this document it had nēn- with long ē in its inflected forms as well (PE21/23). In The Etymologies of the 1930s, however, uninflected nén “water” had a stem form of nen- with short e (Ety/NEN), and the reasons for this variation was discussed in Primitive Quendian Structure: Final Consonants from 1936, the nominative/objective distinction noted above (PE21/64). This seems to be the paradigm Tolkien stuck with thereafter, as evidenced by S. nen “water” rather than ✱✱nîn.