The bus driver starts his work at 5 am every morning.

bus 是名词，意思是"公共汽车"。 driver 是名词，由动词 drive（驾驶）加后缀 -er 构成，表示"驾驶的人"。 bus driver 指"公交车司机"，即驾驶公共汽车的专业驾驶员。