þríhljóð (Icelandic) comes from Icelandic hljóð, from Old Norse hljóð, from Proto-Germanic hleuþą, from Proto-Indo-European ḱlew-to-, from Proto-Indo-European ḱlew-, from Proto-Indo-European ḱel- — to cover; to incline.
þríhljóð (Icelandic): triphthong