I swear to do it (9)
I believe the answer is:
blaspheme
'to do it' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how they can define each other.
'i swear' is the wordplay.
I cannot really see how this works, but
'i' could be 'me' and 'me' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for blaspheme that I've seen before include "Say irreverent things about God" , "Utter obscenities or profanities" , "Speak irreverently about God" , "Speak profanely" , "Swear" .)