Both are heads. Literally. The word remains in English as a cob, known in cobblestones (each has a round head) or a cape, which is also a headland, and that’s the Icelandic word: hæð, or head, or height. Remember that for the culture that settled this magical place, these really were heads. And so they remain.
Troll, Just Hatched, at Dimmu Borgir