§ Annerchin ’Goblin Gate’ (RS:416,432)
The first element is most probably #ann ’gate’, derived from AD- ’entrance, gate’ via adnō > *and, ann. Compare also Early Noldorin ann ’door’ (PE13:137).
The latter element looks like orch ’goblin’ (ÓROK-) with the plural ending -in. Ilkorin affects o > u in the plural, e.g. thorn ’eagle’ > pl. thurnin (THOR,THORON, VT46:19), but also o > e in talum ’ground, floor’ > pl. telmin (TAL-, TALAM). Pl. -in can be observed in Noldorin as well, for instance naugol ’dwarf’ > pl. nauglin (NAUK-). The plural form erchin should be probably seen as uninflected genitive in this context. Alternatively it might be the adjectival ending -in, then it would literally be *’the goblinish gate’.
In The Return of the Shadow Annerchion is found (TI:114) with the ending -ion, on which see the note 4.4 at the end.