Caliburnus

Latinization of Old Welsh Caledfwlch, perhaps influenced by calibs, a medieval spelling variant of chalybs (“iron, steel”). First attested in, and likely coined by, Geoffrey of Monmouth (c. 1136).

• (Classical Latin) IPA^(key): [ka.lɪˈbʊr.nʊs]
• (modern Italianate Ecclesiastical) IPA^(key): [ka.liˈbur.nus]

Caliburnus m sg (genitive Caliburnī); second declension

1. (Medieval Latin, Arthurian legend) Excalibur (the legendary sword of King Arthur, having magical properties).
   • c. 1136, Geoffrey of Monmouth, Historia Regum Britanniae IX-X:

     Accinctus etiam Caliburno gladio optimo, et in insula Avallonis fabricato: lancea dexteram suam decorat, quae nomine Ron vocabatur: haec erat ardua lataque lancea, cladibus apta. […] Arma sua nihil eis proficiebant, quin Caliburnus dextera tam virtuosi regis vibratus, cogeret ipsos animas eructare cum sanguine.

     Then girding on his Excalibur, which was an excellent sword made in the isle of Avallon, he graced his right hand with his lance, named Ron, which was hard, broad, and fit for slaughter. […] Their arms were no manner of protection from them against the force with which this valiant prince wielded his Excalibur.

Second-declension noun, singular only.