Outstanding if not actually well done (4)
I believe the answer is:
rare
'outstanding' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rare that I've seen before include "Might steak be" , "Exceptional" , "Very scarce and probably valuable" , "Scarcely seen" , "Meat that's lightly cooked" .)