Nice line ultimately added to summary (7)
I believe the answer is:
precise
'nice' is the definition.
(similar in meaning)
'line ultimately added to summary' is the wordplay.
'line ultimately' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'added to' is a charade indicator (letters next to each other).
'summary' becomes 'precis' (precis is a kind of summary).
'e' put after 'precis' is 'PRECISE'.
Can you help me to learn more?
(Other definitions for precise that I've seen before include "Specific" , "Detailed, exact" , "Express" , "Exact like recipes" , "with accuracy" .)