Give up because you promise to (8)
I believe the answer is:
forswear
'give up' is the definition.
(I've seen this before)
'because you promise to' is the wordplay.
I cannot quite understand how this works, but
'because' could be 'for' (I've seen this in other clues) and 'for' is found within the answer.
'promise' could be 'swear' (as in swearing something is true) and 'swear' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for forswear that I've seen before include "Denounce" , "Retract - recant" , "Renounce upon oath - far worse (anag)" , "Agree to do without" , "Deny on oath" .)