Excalibur
Geoffrey of Monmouth, in his "Historia Regum Britanniae" ("The History of the Kings of Britain", c. 1136), Latinised the name of Arthur's sword as "Caliburnus" (potentially influenced by the Medieval Latin spelling "calibs" of Classical Latin "chalybs", from Greek "chályps" ["χάλυψ"] "steel"). Most Celticists consider Geoffrey's "Caliburnus" to be derivative of a lost Old Welsh text in which "bwlch" (Old Welsh "bulc[h]") had not yet been lenited to "fwlch" (Middle Welsh "vwlch" or "uwlch"). In the late 15th/early 16th-century Middle Cornish play "Beunans Ke", Arthur's sword is called "Calesvol", which is etymologically an exact Middle Cornish cognate of the Welsh "Caledfwlch". It is unclear if the name was borrowed from the Welsh (if so, it must have been an early loan, for phonological reasons), or represents an early, pan-Brittonic traditional name for Arthur's sword.
Excalibur (Arizona)
Excalibur is a formation on the north rim of the Grand Canyon in Coconino County, Arizona. It was named by cartographer and geologist François E. Matthes in 1908 for Excalibur, the legendary sword of King Arthur which was given to him by the Lady of the Lake. Other features in the area include the Holy Grail, Guinevere Castle, Elaine Castle, and Galahad Point whose names refer to the Arthurian legend. The name probably refers to a spire near the summit of the promontory which might resemble the handle of Excalibur.