Ogre

Although no monsters are explicitly called Ogres in-game, it has been experimentally verified that Ettins 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".