Setter admits to being writer of poetic form (6)
I believe the answer is:
iambic
'poetic form' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'setter admits to being writer' is the wordplay.
'setter' becomes 'I' (the person that set the crossword).
'admits to' becomes 'am' (I can't justify this - if you can you should give a lot more credence to this answer).
'being writer' becomes 'bic' (kind of pen).
'i'+'am'+'bic'='IAMBIC'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for iambic that I've seen before include "In ti-tum rhythm" , "Consisting of short-long metrical feet" , "Line of poetry with unstressed-stressed syllables" , "Of a metrical foot of two syllables, one short and one long" , "Type of verse" .)