Bound to bust, I'm sure (2,5)
I believe the answer is:
no doubt
'i'm sure' is the definition.
I can't tell whether this definition defines the answer.
'bound to bust' is the wordplay.
'bust' is an anagram indicator.
'bound'+'to'='boundto'
'boundto' anagrammed gives 'NO DOUBT'.
Can you help me to learn more?
(Other definitions for no doubt that I've seen before include "Surely" , "To be sure" , "sign of agreement" , "Almost certainly" , "Bound to, unquestionably" .)