Philosophy piece with weak introductory part (8)
I believe the answer is:
thinking
'philosophy' is the definition.
(thesaurus)
'piece with weak introductory part' is the wordplay.
'piece' becomes 'king' (king is a kind of piece).
'with' means one lot of letters go next to another.
'weak introductory part' becomes 'thin' (I can't justify this - if you can you should give a lot more credence to this answer).
'king' after 'thin' is 'THINKING'.
Can you help me to learn more?
(Other definitions for thinking that I've seen before include "Cogitating" , "Considering in the mind" , "Rational" , "Pondering" , "Take" .)