I took this English course and my employer said, if I pass my exam, he will give me a bonus of fifty pounds.

employer 是由动词 employ（雇佣）加上后缀 -er 构成的名词，表示"雇佣者"，即"雇主"。employ 本身来自拉丁语 implicare（卷入、包含），引申为"使用、雇佣"的意思。