The Black Gate of Mordor (LotR/636), a combination of the element √MOR “black” with annon “gate” (Let/382, SA/annon).
Conceptual Development: In Lord of the Rings drafts from the 1940s, it was first named N. Ennyn Dûr, quickly rejected and replaced by the plural form Mornennyn “Gates of Mordor”. This form then lost its first n to be become Morennyn and finally became the singular Morannon “Black Gate” seen in the published version of The Lord of the Rings (WR/112-3, 122).
mor (from stem mor “dark, black”) + annon (“great door or gate”)