Communication system that's great help when working (9)
I believe the answer is:
telegraph
'communication system' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'great help when working' is the wordplay.
'when working' is an anagram indicator (the letters must work themselves into a new order).
'great'+'help'='greathelp'
'greathelp' with letters rearranged gives 'TELEGRAPH'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for telegraph that I've seen before include "Means of communication" , "It's used for communications over wires" , "A scoreboard" , "paper" , "Daily" .)