Initial repetition (12)
I believe the answer is:
alliteration
'initial repetition' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'initial repetition' is the wordplay.
'initial' becomes 'all' (I am not sure about this - if you are sure you should believe this answer much more).
'repetition' becomes 'iteration' (iteration is a kind of repetition).
'all'+'iteration'='ALLITERATION'
Can you help me to learn more?
(Other definitions for alliteration that I've seen before include "Peter practised poetic ploy perfectly" , "Successive starts sounding similarly" , "verse technique" , "Poetic rhyming device using words with the same initial letter" , "Repeated first letters" .)