English for honrai

I would like to know theost suitable English word for 本来.

Originally? Initially? Before this? Or are there more accurate ones? Thank you.

Zyzzyva,

The "most suitable" translation will depend on the situation and context. There is no one "best" translation.
Check Eijiro for a good list of examples...
http://eow.alc.co.jp/%E6%9C%AC%E6%9D%A5/UTF-8/

One of the most common usages of "honrai" is something like:
この役割は、本来Aさんが果たすべきものだが、今回はBさんが行う。
...where they contrast "the way it should be" against the reality.

In this case, I often do not use a single adverb to express the idea in English, but say:
- The way it should be is that this role is fulfilled by Mr. A, but this time Mr. B is assigned to it
- This role should properly be played by Mr A., but....
... or something like that.