The words of a song upset Cyril (5)
I believe the answer is:
lyric
'the words of a song' is the definition.
(I've seen this in another clue)
'upset cyril' is the wordplay.
'upset' indicates an anagram.
'cyril' anagrammed gives 'LYRIC'.
(Other definitions for lyric that I've seen before include "Airline" , "One barred from native country" , "part of song" , "Text of a popular song" , "Words to a song" .)