彼此用英语是each other。

解释：

each other 英[i:tʃ ˈʌðə(r] 美[itʃ ˈʌðər]

v. （用作动词或介词的宾语） 互相，彼此;

[例句]These two examples duplicate each other.

这两个例子重了。

They support each other in their work.

他们在工作中互相支持。

The scientists have already experimented at each other's test sites.

科学家已经在彼此的实验场所进行了实验。

They are reconciled with each other again.; They are on good terms again.

他们和好了。

The ladies spent some time catching up on each other's health and families

女士们花了点时间叙旧，聊了聊彼此的健康和家庭状况。

We are very familiar with each other.

我们相互之间很熟。