1.(with knuckles)敲；击
He knocked before going in.他进去前先敲了敲门。
2.to knock against sb/sth
(collide)与…冲突；碰撞
He deliberately knocked against her as he left the room.他离开房间时故意撞了她一下。
It was the door knocking against the latch.那是门碰门闩的声音。
3.engine +发出轰隆声
His old truck, knocking and smoking, pulled out of sight.他的旧卡车, 轰隆轰隆冒着烟, 驶出了视线。
4.pipe, radiator +发出噪声
The floorboards squeaked and the pipes knocked.地板吱吱响, 管道也噪声不断。
5.bearing +(尤指引擎的轴承)发出声音