Source : Webster's Revised Unabridged Dictionary (1913)

Gumma \Gum"ma\, n.; pl. {Gummata}. [NL. So called from its gummy
   contents See {Gum}.] (Med.)
   A kind of soft tumor, usually of syphilitic origin.

Source : WordNet®

gumma
     n : a small rubbery granuloma that is characteristic of an
         advanced stage of syphilis
     [also: {gummata} (pl)]