out·work /ˌaʊtˈwɚ/
  外堡;外壘;戶外工作
  Out·work v. t. To exceed in working; to work more or faster than.
  Out·work n. Fort. A minor defense constructed beyond the main body of a work, as a ravelin, lunette, hornwork, etc.
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  outwork
       n : subsidiary defensive structure lying outside the main
           fortified area; "the outworks of the castle"