Greatest, ultimate (7)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
supreme
This clue is a double definition.
'greatest' is the first definition.
(I've seen this before)
'ultimate' is the second definition.
(similar in meaning)
(Other definitions for supreme that I've seen before include "Sovereign" , "Chief" , "Unrivalled" , "Most excellent" , "Crowning" .)