The Collaborative International Dictionary of English v.0.48:

Centurion \Cen*tu"ri*on\, n. [L. centurio, fr. centuria; cf. F.
   centurion. See Century.] (Rom. Hist.)
   A military officer who commanded a minor division of the
   Roman army; a captain of a century.
   [1913 Webster]

         A centurion of the hand called the Italian band. --Acts
                                                  x. 1.
   [1913 Webster]

WordNet (r) 3.0 (2006):

centurion
    n 1: (ancient Rome) the leader of 100 soldiers