Monster secure, it’s reported (5)
I believe the answer is:
titan
'monster secure it's reported' is the definition.
I can't tell whether this defines the answer.
'monster secure it's' is the wordplay.
'monster' becomes 'tan' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'secure' is an insertion indicator (inserted letters are secured inside).
'tan' enclosing 'it' is 'TITAN'.
Can you help me to learn more?
(Other definitions for titan that I've seen before include "Moon of Saturn visited by the Huygens probe" , "Largest satellite of Saturn" , "Taint in a great man" , "Giant of Greek mythology" , "One of the first pantheon of Greek deities" .)