Unimprovable (8)
'unimprovable' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ideal that I've seen before include "Very eager (to see)" , "example" , "just the job" , "Pattern" , "(the best one can get)" .)
(Other definitions for ultimate that I've seen before include "The final point" , "Last, final or extreme" , "something extreme" , "Utmost; last" , "Last possible, final" .)