Expert in A-section? (5)
I believe the answer is:
adept
'expert' is the definition.
(synonyms)
'a-section?' is the wordplay.
'section?' becomes 'dept' (short for department).
'a'+'dept'='ADEPT'
'in' is the link.
(Other definitions for adept that I've seen before include "Deacon" , "One highly skilled could be taped" , "One very skilled at work" , "Completely skilled" , "Having the required skills" .)