it is impossible to make more than the wildlest guess at how many they kill中的more than 做什么词性

it is impossible to make more than the wildlest guess at how many they kill
中的more than 做什么词性

意思应该是：
他们杀了多少人?恐怕我们只能凭空猜测一下了.
其实我觉得什么词性并布重要把,more than,我觉得可以解释为,只能,这个句子其实是一个否定,nothing more than,你试着理解一下