The Collaborative International Dictionary of English v.0.48:

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. Guelphic