New heart for the world (5)
I believe the answer is:
earth
'the world' is the definition.
('earth' can be a synonym of 'world')
'new heart' is the wordplay.
'new' indicates an anagram.
'heart' with letters rearranged gives 'EARTH'.
'for' acts as a link.
(Other definitions for earth that I've seen before include "Solid ground" , "Badger or fox burrow" , "Ground - globe - soil" , "underground shelter" , "cost of which is very high" .)