In favour of reducing support (3)
I believe the answer is:
pro
This might be a double definition.
'in favour of' is the first definition.
(being pro a particular cause)
'reducing support' is the second definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for pro that I've seen before include "Golfer" , "For; non-amateur" , "gets paid to play?" , "Skilled" , "In favour of; advantage" .)