Poem composed by Cyril (5)
I believe the answer is:
lyric
'poem' is the definition.
(lyric poem is a kind of poem)
'composed by cyril' is the wordplay.
'composed by' indicates anagramming the letters (I've seen this in other clues).
'cyril' with letters rearranged gives 'LYRIC'.
(Other definitions for lyric that I've seen before include "Expressing poetical emotions" , "A song or poem" , "Poem - verse - London theatre" , "having a light quality" , "(Of poetry) expressing emotion" .)