Look after thinker (4)
I believe the answer is:
mind
I believe this is a double definition.
'look after' is the first definition.
(thesaurus)
'thinker' is the second definition.
('mind' can be a synonym of 'thinker')
(Other definitions for mind that I've seen before include "Seat of the faculty of reason" , "remember" , "Consciousness" , "Look after" , "This can be made up" .)