Terribly simple drives (6)
I believe the answer is:
impels
'drives' is the definition.
(I've seen this in another clue)
'terribly simple' is the wordplay.
'terribly' indicates anagramming the letters.
'simple' with letters rearranged gives 'IMPELS'.
(Other definitions for impels that I've seen before include "Spurs" , "Urges or drives to do something" , "Urges forward" , "Drives on in simple way" , "Forces, urges to action" .)