WordWeb Online

1. A struggle (usually prolonged) between competing entities in which neither side is able to win
   "the hope that his superior campaigning skills would make a difference evaporated in the realization that electioneering had become a form of trench warfare"
    
2. A type of armed combat in which the opposing troops fight from trenches that face each other
   "instead of the war ending quickly, it became bogged down in trench warfare"

Type of: armed combat, combat, war, warfare

Encyclopedia: Trench warfare