"Yelling horn." The horn of the god Heimdallr, according to Völuspá, which is the only poem that mentions it by name:
- Mim's sons dance,
- but the central tree takes fire,
- at the resounding
- Loud blows Heimdall,
- his horn is raised;
- Odin speaks with Mim's head.
Earlier in the same poem, the völva says that she knows that the horn lies hidden under "the heaven-bright holy tree" (i.e. Yggdrasil). In older editions the word hljóð is translated as "horn" while in more recent editions it is translated as "hearing."
Snorri Sturluson in Gylfaginning (27) says that at the time of Ragnarök, Heimdallr shall rise up and sound the Gjallerhorn, and its blast shall be heard throughout all worlds. It will awaken the gods, and they shall hold council together. In chapter 15 however, Snorri refers to it as a drinking horn and associates it with Mímir, who receives his wisdom by drinking of the Mímisbrunnr from the Gjallarhorn.
- Gylfaginning, 15, 27, 51.
- Völuspá, 31, 47.