"Travelers in the forests of our land have oft been fooled into thinking they have drawn near to a group of fellow explorers when they encounter an Ettin, for these two-headed monstrosities have been known to carry on heated discussions with themselves. An Ettin invariably abandons its dialogue when it hath the chance to attack an adventurer."
—Ultima I Bestiary
Multiple-headed trolls receive frequent mention in Scandinavian stories, yet the two-headed monster with the name, "ettin" is not common in European folklore. There is a traditional Scottish tale of the Red Etin (spelled with one "t"). This monster had 3 heads and does not seem to appear outside of this one specific story. Two-headed ettins have long been a staple of the Dungeons & Dragons world. Doubtless, this monster is another example of the writers of the Utima series looking to D&D for inspiration.
The reader does not directly encounter an ettin in Tolkein's books. However, reference is made to the existence of multi-headed trolls.
"Yes, I am afraid trolls do talk like that, even those with only one head each." —The Hobbit, Chater II, Roast Mutton
There is another probable allusion to ettins in the place-name, "The Ettenmoors," a mountainous region north of Rivendell. This is an area known to be populated by trolls.
Mirliton makes a very nice two-headed orc that could very well be an ettin. I'm not sure how big it is. I'm getting one the next time I make an order.