Cyril’s rewritten song (5)
I believe the answer is:
lyric
'song' is the definition.
(I've seen this before)
'cyril's rewritten' is the wordplay.
'rewritten' is an anagram indicator.
'cyril' anagrammed gives 'LYRIC'.
(Other definitions for lyric that I've seen before include "Short poem of songlike quality" , "Expressing the poet's emotions" , "A song or poem" , "Of poetry that expresses the poet's feelings" , "Of poetry that expresses thoughts and feelings" .)