World having change of heart (5)
I believe the answer is:
earth
'world' is the definition.
(I know that world can be written as earth)
'change of heart' is the wordplay.
'change of' is an anagram indicator (the letter order is changed).
'heart' anagrammed gives 'EARTH'.
'having' acts as a link.
(Other definitions for earth that I've seen before include "Huge cost" , "Badger or fox burrow" , "Land" , "Heart (anag)" , "Badger's burrow" .)