Foe of Doctor Who (5)
I believe the answer is:
dalek
'foe of doctor who' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dalek that I've seen before include "Doctor Who creature" , "Croaky-voiced exterminator" , "Alien enemy" , "Alien creation" , "Foe of Dr Who" .)