Philosophy of the Parisian boxer, seldom lacking guts (7)
I believe the answer is:
dualism
'philosophy' is the definition.
(dualism is a kind of philosophy)
'of the parisian boxer seldom lacking guts' is the wordplay.
'of the parisian' becomes 'du' ('of the' in French, eg in Paris).
'boxer' becomes 'Ali' (Muhammad Ali).
'lacking guts' says to hollow out the word (remove centre letters).
'seldom' with its middle removed is 'sm'.
'du'+'ali'+'sm'='DUALISM'
(Other definitions for dualism that I've seen before include "Belief in two basic entities" , "Division into two opposed aspects" , "Eg, what Yin and Yang represent" .)