Essentially abstract Arcadian form of folk music (4)
I believe the answer is:
trad
'folk music' is the definition.
'trad' can be an answer for 'music' (trad is a kind of music). I am unsure of the 'folk' bit.
'essentially abstract arcadian form' is the wordplay.
'essentially' indicates the central letters.
'abstract' becomes 'title' (title is a kind of abstract).
'arcadian form' becomes 'rad' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The central letter of 'title' is 't'.
't'+'rad'='TRAD'
'of' is the link.
Can you help me to learn more?
(Other definitions for trad that I've seen before include "(Of jazz) traditional" , "Style of jazz" , "Type of jazz or folk" , "Classical (abbr)" , "Conventional (jazz)" .)