J.R.R. Tolkien>
The Lord of the Rings
Orthanc was the tower built in the middle of the Ring of Isengard by the early Gondorians. It was made of unbreakable stone and rose more tha 500 feet into the air. It laid empty for quite some time until in the year 2759 of the Third Age, the Istari Saruman was allowed to inhabit it. The Steward of Gondor was hoping that the Wizard would help guard the area from Sauron, but Saruman used it as a base to build his army of Orcs and other evil creatures. During the War of the Ring, Isengard was destroyed by the Ents, but Orthanc was unharmed because of the rock it was made from. As the name of its location suggests, Orthanc was located near the source of the river Isen.
The word 'Orthanc' can be translated with many different meanings. If it is translated as if it were Elvish, it would mean something like 'Mountain of Teeth' or 'Mount Fang'. It is more likely, however, that Orthanc comes from the Old English word orþanc, which is usually taken to mean 'Cunning Mind.' Tolkien never specified which meaning he gave to Orthanc, or even if it had one particular meaning, so it might even have a sort of double meaning.