Source : Webster's Revised Unabridged Dictionary (1913)

Outwork \Out*work"\, v. t.
   To exceed in working; to work more or faster than.

Outwork \Out"work`\, n. (Fort.)
   A minor defense constructed beyond the main body of a work,
   as a ravelin, lunette, hornwork, etc. --Wilhelm.

Source : WordNet®

outwork
     n : subsidiary defensive structure lying outside the main
         fortified area; "the outworks of the castle"