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.
Excalibosaurus
Excalibosaurus (meaning "Excalibur's lizard") is a monotypic genus of marine prehistoric fish-like reptiles (ichthyosaurs) that lived during the Sinemurian stage (approximately 196.5 ± 2 Ma to 189.6 ± 1.5 Ma (million years ago)) of the Early Jurassic period in what is now England. It is characterized by the extreme elongation of the rostrum, with the lower jaw about three fourth of the length of the upper jaw, giving the animal a swordfish-like look. The only known species is "Excalibosaurus costini".