[1] : The Collaborative International Dictionary of English v.0.48

xp \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.
      webster 1913 suppl.
see also:
constantinian symbol monogram labarum 

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