Undone? (4)
I believe the answer is:
rare
'undone?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rare that I've seen before include "Not well done!" , "Seldom seen or met" , "Very lightly cooked, meat say" , "Ben Jonson was considered so" , "Exceptionable" .)