Not only highly expert, this board is right! (4)
I believe the answer is:
star
'not only highly expert' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'board is right' is the wordplay.
'board' becomes 'st' (I am not sure about this - if you are sure you should believe this answer much more).
'is right' becomes 'ar' (I've seen this in other clues).
'st'+'ar'='STAR'
'this' is the link.
Can you help me to learn more?
(Other definitions for star that I've seen before include "Sirius, eg" , "Top performer" , "eg The sun" , "Five-pointed celestial body" , "E.g.Sirius" .)