Ogre

Although no monsters are explicitly called Ogres in-game, it has been experimentally verified that Ettins, Jotun and Yeti are in fact Ogres. Some shields give extra armor against attacks from Ogres and the following weapons inflict extra damage against them:
 * Ogre-Slaying Knife
 * Weapons with the "of Ogreslaying" upgrade

Trolls, Giants, and Oni all fit various meanings of the common term "Ogre," but are not affected by any of the above.