As said by some seasider on stage? (5)
I believe the answer is:
aside
'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 seasider' is the wordplay.
'ASIDE' is hidden in amongst the letters.
However, I'm not sure how the hidden word is indicated.
'on' is the link.
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" .)