With express post initially dropped speed is perhaps extra (7)
I believe the answer is:
edition
'with express' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for edition that I've seen before include "Issue of a book" , "Volume" , "in printed form" , "Copies of book printed from one set of type" , "Number of copies printed at one time" .)