The Collaborative International Dictionary of English v.0.48:

Bedeguar \Bed"e*guar\, Bedegar \Bed"e*gar\, n. [F., fr. Per.
   b[=a]d-[=a]ward, or b[=a]d-[=a]wardag, prop., a kind of white
   thorn or thistle.]
   A gall produced on rosebushes, esp. on the sweetbrier or
   eglantine, by a puncture from the ovipositor of a gallfly
   (Rhodites ros[ae]). It was once supposed to have medicinal
   properties.
   [1913 Webster]