/luːˈten.ənt/
If you refer to someone as a person’s lieutenant, you mean they are that person’s assistant, especially their main assistant, in an organization or activity. [usu poss N]
He was my right-hand man, my lieutenant on the field, a cool, calculated footballer.
他是我的得力助手，球场上的代理人，是一个冷静而有头脑的足球运动员。
an officer of middle rank in the army, navy, or air force （陆军）中尉；（海军或空军）上尉
Lieutenant Paul Fisher
保罗 · 费希尔陆军中尉