Fire endlessly to drive away (4)
I believe the answer is:
shoo
'drive away' is the definition.
(shooing is a kind of driving away)
'fire endlessly' is the wordplay.
'fire' becomes 'shoot' (shooting is a kind of firing).
'endlessly' means to remove the last letter.
'shoot' with its final letter taken off is 'SHOO'.
'to' acts as a link.
(Other definitions for shoo that I've seen before include "Exclamation used to chase away animals" , "Scat!" , "Buzz off!" , "Drive away" , "word of dismissal" .)