each other:互相,彼此之间。
强调“彼此”,用于两者之间。
例:Tom and David share their lunch with each other everyday.
one another:「一个……其他……」适用于三者。后常有「the third/the other」.
例:There are three pens on the desk.One is blue,another is yellow,the third(=the other) is red.
希望对你有所帮助。
each other表示两者之间,而one another则至少是三者。