Sickly pale (3)
I believe the answer is:
wan
'sickly pale' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wan that I've seen before include "Pale as from illness" , "Pale and weak-looking" , "Pale, looking exhausted" , "Lacking colour" , "Looking pale and sickly" .)