⋄ Lonnath Ernin (WR:294)
This is an earlier name of Harlond, a haven south of Minas Tirith.
In the widely known Hiswelóke’s Sindarin dictionary (2.0) a plausible interpretation of ernin as being the plural of arnen *’royal’ < *arnina is proposed (cf. ƷAR-). Lonnath must be the collective plural of lond ’haven’, in The Etymologies N. lhonn means ’narrow pass, strait, pass’ (LOD-), but later S. lond, lonn ’haven’ < LON (VT42:10).
The problematic point (also discussed there) is that there are also nearby hills called Emyn Arnen, where arnen would stand in the singular qualifying pl. emyn < amon ’hill’ (AM2-). This fact, according to Tolkien’s analysis of this name in VT42:17, means that arnen cannot be a Sindarin adjective, but instead may contain wrongly used ar- ’beside’ (which in this meaning is Quenya, not Sindarin) + nen ’water’, thus ’hills beside the water’. But then Lonnath Ernin would not make much sense.
Perhaps the external development of these forms can be summarized as following: At first Tolkien thinks of arnen *’royal’, pl. ernin and calls the haven by that name, but then abandons it, calling the haven Harlond and the nearby hills the ’Hills of Haramon’ (see below). Later he decides that arnen should be an obscure word and changes the name of the hills to Emyn Arnen.