One aspect of things actors are deaf to (5)
I believe the answer is:
aside
'things actors are deaf to' is the definition.
I can't tell whether this defines the answer.
'one aspect' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'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 "In reserve -- confidential remark" , "Line spoken to theatre audience" , "Aides (anag.)" , "Privately, apart" , "Actor's line directed solely to audience" .)