Great Elgar composition (5)
I believe the answer is:
large
'great' is the definition.
(similar in meaning)
'elgar composition' is the wordplay.
'composition' is an anagram indicator (letters arranged or composed in a different order).
'elgar' anagrammed gives 'LARGE'.
(Other definitions for large that I've seen before include "Of great size" , "broad" , "Strapping" , "One has liberty to be at it" , "Big, outsize" .)