N. Mornvenniath loc. “Black Mountains”
A variant name of Eredvyrn “Black Mountains” (itself a precursor to Ered Nimrais) appearing in Lord of the Rings drafts from the 1940s (TI/124). Partrick Wynne suggested it is a combination of morn “black” and the lenited class-plural of ment “point”, or possibly ending with iath “fence” (https://groups.yahoo.com/neo/groups/lambengolmor/conversations/messages/799).
References ✧ TI/124; TII