… very different partner in philosophy? (8)
I believe the answer is:
thinking
'philosophy?' is the definition.
(thesaurus)
'very different partner in' is the wordplay.
I cannot quite see how this works, but
'partner' could be 'n' and 'n' is found in the answer.
'in' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for thinking that I've seen before include "Fancying" , "Pondering" , "Rational" , "Mental process" , "giving opinion" .)