After repeat performance, Diamond gradually tailed off (7)
I believe the answer is:
tapered
'gradually tailed off' is the definition.
I can't judge whether this defines the answer.
'after repeat performance diamond' is the wordplay.
'after' is a charade indicator (letters next to each other).
'performance' indicates anagramming the letters.
'diamond' becomes 'd' (this could be a standard abbreviation which I don't know about).
'repeat' with letters rearranged gives 'tapere'.
'tapere' put next to 'd' is 'TAPERED'.
Can you help me to learn more?
(Other definitions for tapered that I've seen before include "Predate (anag)" , "Gradually narrowing" , "came to the point" , "Pointed" , "got slimmer" .)