Cardinal I introduced to bishop perhaps (4)
I believe the answer is:
main
'cardinal' is the definition.
(thesaurus)
'i introduced to bishop perhaps' is the wordplay.
'introduced to' indicates putting letters inside.
'bishop perhaps' becomes 'man' (bishop is a kind of man).
'i' inserted into 'man' is 'MAIN'.
(Other definitions for main that I've seen before include "Dominant" , "river in Germany" , "associated with the Spanish?" , "Chief - principal electricity cable" , "source of gas" .)