noun · a large organized military unit, such as a corps, or a specific branch of service

这支主力军在关键时刻发起了进攻。

idiom, verb, noun · relating to the armed forces, soldiers, or military affairs

他在高中毕业后选择报名参军。

verb · to put the opponent's king or commander in check in a board game like chess or xiangqi; by extension, to challenge or put someone in a difficult position

这一着棋直接军了对方的老将。