Having written, to cancel (6)
I believe the answer is:
delete
'cancel' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for delete that I've seen before include "'Erase, remove (6)'" , "Cancel, erase" , "Take out" , "Expunge, erase" , "Obliterate" .)