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

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "centurion":
   C, NCO, acting corporal, acting sergeant, bicentenary,
   bicentennial, cental, centare, centenarian, centenary, centennial,
   centennium, centigram, centimeter, centipede, centistere, centred,
   centref, centrev, centumvir, centumvirate, century,
   chief warrant officer, color sergeant, corporal, cwt,
   first sergeant, gross, havildar, hecatomb, hundred, hundredweight,
   lance corporal, lance sergeant, long hundred, master sergeant,
   mess sergeant, naik, noncom, noncommissioned officer, one C,
   platoon sergeant, sarge, sergeant, sergeant first class,
   sergeant major, sesquicentenary, sesquicentennial, staff sergeant,
   technical sergeant, tercentenary, tercentennial, top sergeant,
   topkick, warrant officer



Easton's 1897 Bible Dictionary:

Centurion
   a Roman officer in command of a hundred men (Mark 15:39, 44,
   45). Cornelius, the first Gentile convert, was a centurion (Acts
   10:1, 22). Other centurions are mentioned in Matt. 8:5, 8, 13;
   Luke 7:2, 6; Acts 21:32; 22:25, 26; 23:17, 23; 24:23; 27:1, 6,
   11, 31, 43; 28:16. A centurion watched the crucifixion of our
   Lord (Matt. 27:54; Luke 23:47), and when he saw the wonders
   attending it, exclaimed, "Truly this man was the Son of God."
   "The centurions mentioned in the New Testament are uniformly
   spoken of in terms of praise, whether in the Gospels or in the
   Acts. It is interesting to compare this with the statement of
   Polybius (vi. 24), that the centurions were chosen by merit, and
   so were men remarkable not so much for their daring courage as
   for their deliberation, constancy, and strength of mind.", Dr.
   Maclear's N. T. Hist.