Naive, as some popes were (8)
I believe the answer is:
innocent
'naive' is the definition.
(similar in meaning)
'as some popes were' is the wordplay.
I cannot really see how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is present in the answer.
The remaining letters 'nocent' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for innocent that I've seen before include "Harmless or guiltless" , "Giovanni Lotario de' Conti?" , "Without blame or guilt" , "otherworldly?" , "Virgin" .)