For example:
* "He gave a replying nod to her question."
* "The replying message was short and to the point."
However, depending on the context, other adjectives could be used to describe a reply, such as:
* Prompt
* Swift
* Courteous
* Detailed
* Concise
* Evasiveness
* Reassuring
It all depends on what specific characteristic of the reply you want to highlight.