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.
Geoffrey Gaimar
A version of Havelok the Dane occurs at the beginning of "L'Estoire des Engles", which must have originally been interpolated in between the history of the Britons and the history of the English, serving as a bridge. Unlike the Middle English version of the legend, Gaimar's version connects Havelok to King Arthur (making Arthur responsible for destroying the Danish kingdom that Havelok was to inherit.) Added to this is a mention of the sword Calibur (Excalibur), demonstrating Gaimar's knowledge of Galfridian legendary history that predated the advent of Wace's "Brut".