让某人 duck 的意思是让此人把头低下或弯下腰来躲避某物的碰击。

例句

As I walked in the door someone shouted "Duck!" But it was too late and I hit my head.

The batsman shouted "Duck!" as he hit the ball right at where the spectators were standing.

请注意

短语 duck out 的意思是逃避、躲开做某事。

Sorry, I've got to duck out of this meeting, I've got too many other things to do.