Wordnet 3.0
NOUN (1)
1. 
 subsidiary defensive structure lying outside the main fortified area; 
- Example: "the outworks of the castle"
The Collaborative International Dictionary of English v.0.48:
Outwork \Out*work"\, v. t.
   To exceed in working; to work more or faster than.
   [1913 Webster]
The Collaborative International Dictionary of English v.0.48:
Outwork \Out"work`\, n. (Fort.)
   A minor defense constructed beyond the main body of a work,
   as a ravelin, lunette, hornwork, etc. --Wilhelm.
   [1913 Webster]
WordNet (r) 3.0 (2006):
outwork
    n 1: subsidiary defensive structure lying outside the main
         fortified area; "the outworks of the castle"