Met to compose choral work (5)
I believe the answer is:
motet
'choral work' is the definition.
(I've seen this in another clue)
'met to compose' is the wordplay.
'compose' indicates an anagram.
'met'+'to'='metto'
'metto' anagrammed gives 'MOTET'.
(Other definitions for motet that I've seen before include "work by Tallis, for example" , "Piece for choir" , "Certain one is morally superior" , "Church choral composition" , "Short sacred choral piece" .)