A change of heart for one mother (5)
I believe the answer is:
earth
'one mother' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'a change of heart' is the wordplay.
'a change of' indicates an anagram.
'heart' is an anagram of 'EARTH'.
'for' is the link.
Can you help me to learn more?
(Other definitions for earth that I've seen before include "It is necessary to clear" , "Fox's underground lair" , "our home" , "wire" , "Familiar example of 1 Across" .)