If we look at the origins of the words "troll" and "ogre" there is a difference in meaning. Troll comes from Old Norse for "demon, fiend". Ogre comes from Old French for "man eating giant". There is speculation that ogre might even be derived from the Latin "god of the underworld". There are some overlapping definitions of the two words, but "man eating" is only applied to ogres. Trolls can evidently be either giants or dwarves. There is entirely separate mythology involved with these two creatures as well. Trolls are Norse legend, while ogres may have been "invented" in Southern Europe. If the ancient Danes didn't buy into the "ogre" mythology they wouldn't necessarily have a directly translated word for that particular creature. "Troll" seems to have been a general catch-all word for evil supernatural beings, originally in Swedish, trolla - "to charm, bewitch;" and in Old Norse, trolldomr - "witchcraft." Troll-bull, a supernatural being in the form of a bull, and boar-trolls appear in the Viking sagas. (see Online Etymology Dictionary). You might want to try translations for "demon", "fiend" and "giant" into Danish to see what you get.