What is "thunderdell"

Thunderdell, also recorded as Thunderdel, Thunderel, Thundrel, Thunderdale, or Thunderbore, was a two-headed giant of Cornwall slain by Jack the Giant-Killer in the stories of Tabart and others.

Jeff Rovin's The Encyclopedia of Monsters (New York: Facts on File, 1989) misspells Thunderdell as "Thunderel", and after describing him, proceeds to tell the basic story of Jack and the Beanstalk with no further mention of "Thunderel", despite being the title of the entry. He then refers readers to Cormoran.