English, from Latin "curled (hair)"; an early spelling variant of Crispin.
Note that many old documents and some later ones replaced the first few letters with an "X": e.g. "Xpian". In the older documents in Latin an ending -us was normally added, and modified as a Latin case ending. At that time, Crispin & Crispian were generally written as Crispianus or Xpianus.