As said by some seasider on stage? (5)
I believe the answer is:
aside
'seasider on stage?' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
'as said by some' is the wordplay.
'as said' becomes 'side' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' means one lot of letters go next to another.
'some' becomes 'a'.
'side' put after 'a' is 'ASIDE'.
Can you help me to learn more?
(Other definitions for aside that I've seen before include "Privately, apart" , "In reserve -- confidential remark" , "Out of other people's hearing" , "Whispered comment" , "Quiet words spoken" .)