One aspect of stage delivery (5)
I believe the answer is:
aside
'stage delivery' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'one aspect' is the wordplay.
'one' becomes 'a'.
'aspect' becomes 'side' (side is a kind of aspect).
'a'+'side'='ASIDE'
'of' is the link.
Can you help me to learn more?
(Other definitions for aside that I've seen before include "Actor's covert line" , "Line spoken to theatre audience" , "secretly" , "Separately" , "(Turn) off main path" .)