Different arrangement, as carthorse would be for orchestra (7)
I believe the answer is:
anagram
'different arrangement' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'carthorse would be for orchestra' is the wordplay.
I cannot quite understand how this works, but
'be' could be 'am' and 'am' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'as' acts as a link.
Can you help me to learn more?
(Other definitions for anagram that I've seen before include "Word rearranging another's letters" , "new order, literally" , "Word play" , "Eg "oscillation" of "colonialist"" , "'Master' of 'stream', say" .)