skirmisher
  從事小爭鬥者,斥候兵,前衛
  Skir·mish·er n. One who skirmishes. Specifically: pl. Mil. Soldiers deployed in loose order, to cover the front or flanks of an advancing army or a marching column.
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  skirmisher
       n : someone who skirmishes (e.g., as a member of a scouting
           party)