Source : Webster's Revised Unabridged Dictionary (1913)

Underdo \Un`der*do"\, v. i.
   To do less than is requisite or proper; -- opposed to overdo.
   --Grew.

Underdo \Un`der*do"\, v. t.
   To do less thoroughly than is requisite; specifically, to
   cook insufficiently; as, to underdo the meat; -- opposed to
   {overdo}.