A root mentioned in Primitive Quendian Structure: Final Consonants from 1936 as the basis for the 1930s genitive suffix ᴹQ. -n. In later writings, the Quenya genitive suffix became Q. -o, and the dative suffix -n was given a new etymology from √NA/ANA, so likely ᴹ√ENE fell out of Tolkien’s favor for this particular use.
Middle Primitive Elvish
ne
root. *in
nē
adverb. was; then, ago
nĕ
suffix. ?genitive
-nē
suffix. past suffix
ene
root. ?genitive
lep(e)ne
noun. five
ndē̆-
prefix. in, inside
kwǣnē
noun. small gull, petrel
lepen
root. five
mī/imi
root. in, inside
(n)di
root. in
eʒ-
verb. to be
imi
root. in
kalrondō
noun. hero
kar-
verb. make, do, are [sic, should be ‘is’] making it
lepek
root. five
ta
root. that
yē
root. to be
ē
root. to be
ī
root. to be
A rejected root in The Etymologies of the 1930s with a strengthened form ✱ndē̆ serving as the basis for the prefix in N. nestag- “insert”, possibly related to ᴹ√NED “middle” (EtyAC/NĒ̆). The strengthened form may have been replaced by the root ᴹ√(N)DI “in” (EtyAC/NDI), but in later writing ✶ndī was given the meaning “beneath, not touching, under” (PE17/95). Despite the rejection of the root, the verb N. nestag- “insert” remained unmodified under the root ᴹ√STAK (Ety/STAK), and there is further evidence for the ne- prefix in the verb N. neledh- “enter” appearing on the 1936 draft of Thror’s Map from this same time period (TAI/150).
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is worth retaining this (Noldorin and Sindarin-only?) prefix ne- “in”.