Middle EnglishExcalaber, from Old FrenchEscalibor, Escaliborc, prothetic form of Calliborc, alteration of Calibourne, from Medieval LatinCaliburnus (Geoffrey of Monmouth, ca. 1136), influenced by calibs ‘steel’ (for chalybs), alteration of Old Welsh*Caledbulch (cf. modern Caledfwlch), compound of caled ‘hard’ and bwlch ‘cleft, crack’. Related to the Irish legendary sword Caladbolg, literally ‘hard-belly’, i.e. ‘voracious’.