\XP\ [Belongs here in appearance only.]
The first two letters of the Greek word XRISTOS, Christ; --
an abbreviation used with the letters separate or, oftener,
in a monogram, often inclosed in a circle, as a symbol or
emblem of Christ. It use as an emblem was introduced by
Constantine the Great, whence it is known as the
{Constantinian symbol}, or
{monogram}. See {Labarum}.