The interpretation of the name Hyarmentir as 'southern watch' seems clear, though it is difficult to fully parse its meaning. The reason behind 'southern' or 'south' in its name is obvious, as it lay to the south of Valinor, but 'watch' is more problematic. The tir element usually implies a watch-tower or guard post, but in this case the Silmarillion goes out of its way to point out that the Valar did not maintain any watch in this area. Morgoth and Ungoliant stood on the summit of this mountain and looked out over Valinor before they attacked the Two Trees, and so perhaps it only subsequently acquired the name Hyarmentir in recollection of this event.

The geography shown on this map comes from a sketch map identified as 'Map V' in volume IV of The History of Middle-earth. This is a rough map from early in the development of Tolkien's work, but it does at least give us an impression of the arrangement of mountain ranges in this part of the world. Unfortunately, Hyarmentir is not specifically marked on that map, so identifying its exact location is problematic.

Our only clues come from the text of The Silmarillion, which states that it lay far to the south of Taniquetil, and that, from its summit, the city of Valmar lay northward, while the woods of Oromë and the fields beyond lay to the west. When Melkor set out from its peak into Valinor he '...leapt swiftly down the long western slopes' (Quenta Silmarillion 8, Of the Darkening of Valinor). In combination, these references imply that Hyarmentir must have stood at a point eastward of the most southerly parts of Valinor.