Source : Webster's Revised Unabridged Dictionary (1913)

Guelph \Guelph\, Guelf \Guelf\ (gw[e^]lf), n. [It. Guelfo, from
   Welf, the name of a German family.] (Hist.)
   One of a faction in Germany and Italy, in the 12th and 13th
   centuries, which supported the House of Guelph and the pope,
   and opposed the Ghibellines, or faction of the German
   emperors.