Source : Webster's Revised Unabridged Dictionary (1913)

Indiction \In*dic"tion\, n. [L. indictio: cf. F. indiction. See
   {Indict}, {Indite}.]
   1. Declaration; proclamation; public notice or appointment.
      [Obs.] ``Indiction of a war.'' --Bacon.

            Secular princes did use to indict, or permit the
            indiction of, synods of bishops.      --Jer. Taylor.

   2. A cycle of fifteen years.

   Note: This mode of reckoning time is said to have been
         introduced by Constantine the Great, in connection with
         the payment of tribute. It was adopted at various times
         by the Greek emperors of Constantinople, the popes, and
         the parliaments of France. Through the influence of the
         popes, it was extensively used in the ecclesiastical
         chronology of the Middle Ages. The number of indictions
         was reckoned at first from 312 a. d., but since the
         twelfth century it has been reckoned from the birth of
         Christ. The papal indiction is the only one ever used
         at the present day. To find the indiction and year of
         the indiction by the first method, subtract 312 from
         the given year a. d., and divide by 15; by the second
         method, add 3 to the given year a. d., and the divide
         by 15. In either case, the quotient is the number of
         the current indiction, and the remainder the year of
         the indiction. See {Cycle of indiction}, under {Cycle}.

Source : WordNet®

indiction
     n : a 15-year cycle used as a chronological unit in ancient Rome
         and adopted in some medieval kingdoms