Is it ensure, insure, or assure?
16c., forms replacing earlier Christen, from Old English cristen (noun and adjective), from a West Germanic borrowing of Church Latin christianus, from Ecclesiastical Greek christianos, from Christos (see Christ). First used in Antioch, according to Acts xi:25-26. Christian Science as the name of a religious sect is from 1863.
A follower or disciple of Jesus; someone who believes Jesus is the Christ or Messiah. The New Testament mentions that the followers of Jesus were first called Christians within a few years after his death.
the name given by the Greeks or Romans, probably in reproach, to the followers of Jesus. It was first used at Antioch. The names by which the disciples were known among themselves were "brethren," "the faithful," "elect," "saints," "believers." But as distinguishing them from the multitude without, the name "Christian" came into use, and was universally accepted. This name occurs but three times in the New Testament (Acts 11:26; 26:28; 1 Pet. 4:16).