Excellent yet not well done (4)
I believe the answer is:
rare
This clue is a double definition.
'excellent' is the first definition.
(I've seen this in another clue)
'not well done' is the second definition.
(as in a steak)
'yet' acts as a link.
(Other definitions for rare that I've seen before include "Very scarce and probably valuable" , "Very scarce like valuable antique" , "Meat that's lightly cooked" , "few and far between" , "Seldom - unusual" .)