Champion on board is superficial (7)
I believe the answer is:
surface
'is superficial' is the definition.
(similar in meaning)
'champion on board' is the wordplay.
'champion' becomes 'ace' (both can mean a person excelling at something).
'on' means one lot of letters go next to another.
'board' becomes 'surf' (I am not sure about this - if you are sure you should believe this answer much more).
'ace' after 'surf' is 'SURFACE'.
Can you help me to learn more?
(Other definitions for surface that I've seen before include "skin" , "Superficial appearance" , "Outer or upper layer" , "Plane" , "Exterior" .)