Nothing tops excellent end of series (5)
I believe the answer is:
omega
'end of series' is the definition.
(last letter of the Greek alphabet)
'nothing tops excellent' is the wordplay.
I cannot quite understand how this works, but
'nothing' could be 'o' (O resembles 0) and 'o' is found within the answer.
'excellent' could be 'mega' (old-fashioned UK slang for 'very good') and 'mega' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for omega that I've seen before include "Last thing" , "character from Athens" , "symbol of resistance?" , "End of sequence" , "in Greece, the limit!" .)