XIPHURA
Xi*phu"ra, n. pl. Etym: [NL., from Gr. xi`fos sword + (Zoöl.)
Defn: Same as Limuloidea. Called also Xiphosura. X ray. See under
Ray.
XP
XP. [Belongs here in appearance only.]
Defn: 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.
X RAYS; X-RAYS
X rays, or X"-rays`, n. pl.
Defn: The Röntgen rays; — so called by their discoverer because of their enigmatical character.
X-RAY TUBE
X"-ray" tube. (Physics)
Defn: A vacuum tube suitable for producing Röntgen rays.
XYLAMIDE
Xy*lam"ide, n. Etym: [Xylic + amide.] (Chem.)
Defn: An acid amide derivative of xylic acid, obtained as a white crystalline substance.