The world has a change of heart (5)
I believe the answer is:
earth
'the world' is the definition.
('earth' can be a synonym of 'world')
'a change of heart' is the wordplay.
'a change of' indicates an anagram (the letter order is changed).
'heart' with letters rearranged gives 'EARTH'.
'has' is the link.
(Other definitions for earth that I've seen before include "It is necessary to clear" , "underground shelter" , "Our favourite planet" , "electrical safety precaution" , "brownish pigment?" .)