Cyril ruined words for song (5)
I believe the answer is:
lyric
'words for song' is the definition.
(I've seen this before)
'cyril ruined' is the wordplay.
'ruined' indicates an anagram.
'cyril' with letters rearranged gives 'LYRIC'.
(Other definitions for lyric that I've seen before include "One barred from native country" , "A song or poem" , "part of song" , "Cyril (anag.)" , "Poetic lines" .)