Without a present, cancels and drives back (6)
I believe the answer is:
repels
'drives back' is the definition.
('repel' can be a synonym of 'drive back')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for repels that I've seen before include "Drives back or disgusts (6)" , "Forces back" , "Drives away from lepers" , "Disgusts or drives away" .)