A word for “pool” or “lake”, appearing as an element in the name Linaewen “Lake of Birds” (S/119; UT/401). As an independent word it is probably ✱lîn, and it is probably a derivative of the root √LIN of similar meaning (PE17/145, 160).
Conceptual Development: The earliest obvious precursor to this word is ᴱN. lhuin “pool” in Early Noldorin Word-lists of the 1920s (PE13/149). In The Etymologies of the 1930s it appeared as N. lhîn “pool”, a derivative of the root ᴹ√LIN “pool” and cognate to ᴹQ. linya (Ety/LIN¹). Remnants of the ancient y can be seen in its (lenited) class plural liniath in the name N. Hithliniath “Pools of Mist” (Ety/KHIS; LR/262). It cannot be a direct cognate of its Quenya form, however, at it has no signs of a-affection. Christopher Tolkien mentioned the name element lin “pool, mere” in The Silmarillion appendix (SA/lin), though whether it was intended to be a primitive form or a Sindarin word isn’t clear.
Neo-Sindarin: I think it is best to simply adapt the Noldorin form into (Neo) Sindarin as lîn, perhaps derived from primitive ✱linyē and hence with class plural liniath.
_n. _a people of one kind or origin. >> gwaith, rim