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.