Curtana, also Cortana or Courtain, is a latinized form of the Anglo-French curtein, from Latin curtus, 'shortened', used for a ceremonial type of sword. [...] Curtana was also, according to legend, the sword of Ogier the Dane; it bore the inscription "My name is Cortana, of the same steel and temper as Joyeuse and Durendal."
It's also worth noting that Durendal (or Durandal) was an AI in a previous Bungie game, Marathon. Durandal was the sword of Roland, one of Charlemagne's knights. This is one of many connections between Halo and Marathon, although they do not take place in the same universe.