A great egg boiled whole (9)
I believe the answer is:
aggregate
'whole' is the definition.
(aggregate is a kind of whole)
'a great egg boiled' is the wordplay.
'boiled' is an anagram indicator (letters cooked or boiled into a new form).
'great'+'egg'='greategg'
'greategg' anagrammed gives 'ggregate'.
'a'+'ggregate'='AGGREGATE'
(Other definitions for aggregate that I've seen before include "Material mixed with cement to form concrete" , "A whole formed by combining several elements" , "Combine into a whole" , "Material to make concrete, mortar, or plaster" , "The whole amount" .)