Why does 努力 which means "to make a great effort" sound so similar to 奴隸 which means "slave"?
I am not an expert on morphemes and cognates. My two cents, that it is just coincidental. So are other words, such as 输血 and 数学，水饺 and 睡觉，事实 and 石狮. To make it a bit gross, 食 and 屎.