Great help, perhaps, in rapid communication (9)
I believe the answer is:
telegraph
'rapid communication' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'great help perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'great'+'help'='greathelp'
'greathelp' anagrammed gives 'TELEGRAPH'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for telegraph that I've seen before include "Transmission (by wire on poles)" , "paper" , "Signal" , "Means of communication" , "Send message" .)