Top section having skill (5)
I believe the answer is:
adept
'having skill' is the definition.
'top section' is the wordplay.
'top' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'section' becomes 'dept' (short for department).
'a'+'dept'='ADEPT'
(Other definitions for adept that I've seen before include "Very skilful, proficient" , "Proficient - expert" , "One who is very skilful" , "Skilful, expert" , "skilled performer" .)