Almost unique (4)
I believe the answer is:
rare
'almost unique' 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 easily come by like undercooked meat" , "Very lightly cooked, meat say" , "Not often seen - underdone" , "Ben Jonson was considered so" , "Very infrequent, lightly cooked" .)