Stage whisper (5)
I believe the answer is:
'stage whisper' is the definition.
(both can mean a remark heard by an audience)
This is the entire clue.
(Other definitions for aside that I've seen before include "Where one's taken for intimacy" , "Remark by an actor, directly to audience say" , "private" , "(Pushed) out of the way" , "Aides (anag.)" .)