Major Elgar composition (5)
I believe the answer is:
large
'major' is the definition.
(thesaurus)
'elgar composition' is the wordplay.
'composition' is an anagram indicator.
'elgar' anagrammed gives 'LARGE'.
(Other definitions for large that I've seen before include "Gross" , "One has liberty to be at it" , "Little's late partner" , "Strapping" , "Sizable" .)