n.定位焊；紧钉
n.变换航向
动词tack的现在分词形式.
His brother is sharp as a tack; he got100 on every test. 他弟弟十分聪明伶俐，每次考试都得100分。
By tacking about, we were able to avoid the enemy guns. 我们摆动着船帆不停地调转船头，才得以躲过敌人的炮弹。
