Immense Elgar composition (5)
I believe the answer is:
large
'immense' is the definition.
(similar in meaning)
'elgar composition' is the wordplay.
'composition' indicates an anagram.
'elgar' with letters rearranged gives 'LARGE'.
(Other definitions for large that I've seen before include "Bumper" , "Gross" , "Little's late partner" , "Chunky" , "Strapping" .)