Source : Webster's Revised Unabridged Dictionary (1913)

Underbred \Un"der*bred`\, a.
   Not thoroughly bred; ill-bred; as, an underbred fellow.
   --Goldsmith.

Source : WordNet®

underbred
     adj 1: (of persons) lacking in refinement or grace [syn: {ill-bred},
             {bounderish}, {lowbred}, {rude}, {yokelish}]
     2: of inferior or mixed breed; "a cur dog"; "an underbred dog"