Of course I would need to break in (6)
I believe the answer is:
indeed
'of course' is the definition.
(thesaurus)
'i would need to break in' is the wordplay.
'i would' becomes 'id'.
'to break' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'need' with letters rearranged gives 'ndee'.
'id' enclosing 'ndee' is 'INDEED'.
(Other definitions for indeed that I've seen before include "Unquestionably" , "In truth, in fact" , "Really - truly" , "Yes, truthfully" , "Certainly, quite so" .)