Question: I have a system which has the following structure:

Inbound > Open > Pending > Awaiting reply > Ready > Closed

I'd like to use single-words, so the one that sticks out like a sore thumb is "Awaiting reply".

I obviously can't use "Pending" because that's already in use. And "Awaiting" is too similar to "Pending".

Is there a word for "waiting for a reply"?

Answer: 
I think you may have to live with "awaiting reply." Even if you do find a single word that comes close to the same meaning, it is likely to be obscure or not appropriate for the context.

In technical writing, which is how I would classify documenting a process, it is sometimes necessary to sacrifice elegance in favor of making your writing clear and easy to understand quickly with a minimum of mental friction. In this case, your goal is to make your writing "invisible": if the reader "notices" what you've written, that means you've failed. When the reader encounters the labels you've given the process steps, he or she should understand them immediately without a second thought. "Awaiting reply" achieves that goal, whereas a more flowery or clever single-word label may not.
Potentially you could turn the focus around from the expected action of the respondent, to the last action of the maintainer/asker. For example, perhaps one of the following could be used:

* Inquired
* Requested
* Solicited
* Queried

At the moment I'm liking "queried", because it has two syllables, like everything else in the OP's list up until "closed".

Other synonyms for "request information" at [Thesaurus.com](https://www.thesaurus.com/browse/request%20information).