Pengyou

[Aga]

Our teacher asked us:
Why do we write Pengyou (a Friend in Chinese) since "peng" means a friend and also "you" has a familiar meaning?
Is there somebody who can answer my question: why this word has such structure?
Thank You...

[wenming hu]

朋友 is a phrase, consists of two chinese chars. thoung i am a native chinese, i also don't know what the reason is. there are many phrases like this.