Composition — first of Elgar’s symphonies, for example (5)
I believe the answer is:
essay
'composition' is the definition.
(thesaurus)
'first of elgar's symphonies for example' is the wordplay.
'first of' indicates taking the first letters.
'for example' becomes 'say' (I've seen this before).
The initial letters of 'elgar symphonies' is 'es'.
'es'+'say'='ESSAY'
(Other definitions for essay that I've seen before include "Make an effort or attempt" , "Try; short written work" , "Composition, paper, article" , "Short literary piece: attempt" , "Short treatise" .)