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.
Scientology
In April 1938, Hubbard reportedly reacted to a drug used in a dental procedure. According to his account, this triggered a revelatory near-death experience. Allegedly inspired by this experience, Hubbard composed a manuscript, which was never published, with the working titles of "The One Command" or "Excalibur". The contents of "Excalibur" formed the basis for some of his later publications. Arthur J. Burks, who read the work in 1938, later recalled it discussed the "one command": to survive. This theme would be revisited in Dianetics, the set of ideas and practices regarding the metaphysical relationship between the mind and body which became the central philosophy of Scientology. Hubbard later cited "Excalibur" as an early version of Dianetics.