Indiction, a cycle of 15 years instituted by Constantine the Great, and which began on the 24th September 812, the day of his victory over Maxentius; to find the indiction of any year add 1 and divide by 15.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
India-rubber, Caoutchouc * Indium