A sighed utterance? (5)
I believe the answer is:
aside
'utterance?' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'a sighed' is the wordplay.
'sighed' becomes 'side' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'side'='ASIDE'
Can you help me to learn more?
(Other definitions for aside that I've seen before include "Stage whisper" , "kept in reserve" , "Whispered comment" , "Remark by an actor, directly to audience say" , "Line spoken to theatre audience" .)